Jágr was the first Czechoslovak player to be drafted by the NHL without first having to defect to the West; his selection in the NHL draft came as the Iron Curtain was falling. Because of this, after Jágr was selected by the Pittsburgh Penguins with the fifth overall pick in the 1990 NHL Entry Draft, he was able to immediately relocate to North America from Czechoslovakia. When he attended the draft, in Vancouver, he was the first Czechoslovak player present at the NHL draft with his government’s blessings.

Jágr was a supporting player with the powerhouse Penguins that won back-to-back Stanley Cups in 1991 and 1992. He was one of the youngest players in NHL history, at age 20, to score a goal in the Stanley Cup Finals.

Jágr has represented his country many times. In 1994, he and Pittsburgh Penguins teammate Martin Straka arrived in the middle of the 1994 World Championships after Pittsburgh’s elimination from the Stanley Cup playoffs. Czech fans’ expectations were high as Jágr was an NHL star, but before the team was able to integrate him into the team, the Czechs lost their quarterfinal game and were eliminated from tournament. Jágr was also hurt in numerous other games.

The 1996 World Cup of Hockey also did not see Jágr at his best. His performance was hampered by the flu and it only underscored the poor play of the whole team — after losing 7–3 to Finland, 3–0 to Sweden and even 7–1 to a relatively weak Germany, the team did not qualify for the tournament’s playoffs.

Jágr did not play in the 1996, 1999, 2000 nor 2001 World Championships in which the Czech Republic won the gold medals. He was, however, a member of the team at the 2004 World Championship in Prague, where the expectations were high. However, after the team won all the games in the group, they lost in the quarterfinals game, stumbling out of the tournament.

The team’s recent failures, however, were mitigated in 1998 when the Czech Republic won the men’s gold medal in the 1998 Winter Olympics in Nagano, Japan. It was only the third gold medal for Czech or Czechoslovak sportsmen from the Winter Olympics and it is still fondly remembered.

In the 1994–95 season, Jágr won his first Art Ross Trophy after finishing the regular season with the most points in the NHL; he tied Eric Lindros with 70 points but won based on his 32 goals to Lindros’ 29. The next year, Jágr set a record for most points, 149, by a European-born player. Both his 62 goals and 87 assists from that season still stand as career-highs. His 1995–96 totals for assists and points stand as the records for right-wingers in those categories. After the 1997–98 season, Penguins captain Ron Francis signed with the Carolina Hurricanes, leaving Jágr the Penguins’ captaincy. From 1997–98 to 2000–01, Jágr would win four-straight NHL scoring titles. In 1999, he would win the Hart Memorial Trophy as the NHL’s most valuable player, as well as the Lester B. Pearson Award. In 1998, he led the Czech Republic to a gold medal at the 1998 Winter Olympics.

On 30 December 1999, against the New York Islanders, Jágr scored three goals and four assists for a career high seven-point night. He would later match this feat on 11 January 2003 by once again scoring three goals and four assists in a game against the Florida Panthers as a member of the Washington Capitals.

In 2000–01, Jágr was struggling to find his scoring touch and faced criticisms about his relationship with Penguins head coach Ivan Hlinka. With the return of Mario Lemieux from retirement, the Penguins had two superstars, but friction developed between the two; Jágr held the captaincy but many fans regarded Lemieux as the talisman of the team. Additionally, the struggling, medium-market Penguins could, with Lemieux back, no longer hope to afford Jágr’s high salary. Thus, on 11 July 2001, the organization traded him, along with František Kučera, to the Washington Capitals in exchange for Kris Beech, Michal Sivek and Ross Lupaschuk.

Later in 2001, the Capitals signed Jágr to the then-largest contract ever in NHL history at $77 million over seven years, an average annual value of $11 million, with an option for an eighth year. However, Jágr did not live up to expectations in Washington, as the Capitals failed to defend their division title and missed the 2002 Stanley Cup playoffs. For the first time during his tenure with the Capitals, Jágr failed to finish among the NHL’s top scorers, help his team qualify for the Stanley Cup playoffs or make the NHL All-Star Team. During the summer of 2002, the Capitals reunited Jágr with former linemate Robert Lang. In 2002–03, Washington finished sixth overall in the Eastern Conference but lost to the upstart Tampa Bay Lightning in the first round of the 2003 playoffs despite winning the series’ first two games.

Jágr is an Orthodox Christian; he was baptized in 2001 by Prague’s metropolitan. He began to speak more publicly about his faith during his three-year stint in Russia, a historically Orthodox nation.

Although he has repeatedly denied that he has a gambling problem, Jágr admitted in 2003 that he settled debts totaling $950,000 with two internet gambling sites between 1998 and 2002. The first of these incidents centered on Belize-based website CaribSports and its owner, William Caesar, to which Jágr owed $500,000. Sports Illustrated reported that Jágr agreed to make monthly payments to Caesar to settle the debt, and Caesar leaked the story to the press when Jágr stopped making payments. In 2003, the Internal Revenue Service (IRS) filed a $3.27 million lien against him for unpaid taxes for the 2001 tax year. Only a few months before, Jágr had settled a $350,000 claim for taxes dating to 1999. In the summer of 2006, Jágr sued his former accountant over a tax form that was supposed to have been filed in 2003, claiming that the form would have saved him $6 million had it been timely filed.

On 23 January 2004, Jágr was eventually traded to the New York Rangers in exchange for Anson Carter and an agreement that Washington would pay approximately $4 million per year of Jágr’s salary. Jágr also agreed to defer (with interest) $1 million per year for the remainder of his contract to allow the trade to go through.

Jágr has been a long-time supporter of the liberal conservative Civic Democratic Party (ODS), stating in 2004 that he “had always” voted for the party. In the previous election, he appeared on the party’s billboards and was among its sponsors.

Jágr scored his 1,400th point on a power play goal against the Philadelphia Flyers on 2 March 2006, pushing him past Jari Kurri into second place all-time among European-born players. He later passed Stan Mikita to become the all-time leader.

On 18 March 2006, against the Toronto Maple Leafs, Jágr became only the sixth Rangers player in team history to break the 100-point barrier, and became the only Ranger right winger to score 100 points in a season.

On 27 March 2006, against the Buffalo Sabres, Jágr had a goal and an assist, which tied both the Rangers’ single-season goal record of 52 (Adam Graves, 1993–94) and the Rangers’ single season points record of 109 (Jean Ratelle, 1971–72). Two nights later, on 29 March, Jágr passed Ratelle when he assisted on Petr Průcha’s first-period goal against the New York Islanders’ Rick DiPietro. On 8 April, against the Boston Bruins, Jágr scored his NHL-leading 53rd goal of the season, breaking the Rangers’ single-season goals record.

On 5 October 2006, before the first game of the 2006–07 season (against his former team Washington), Jágr was named as the 24th captain in the history of the New York Rangers, replacing Mark Messier, who had retired before the 2005–06 season. Jágr then proceeded to score a goal on his first shift in the game, just under 30 seconds into the new season.

Jágr scored his 600th career NHL goal on 19 November 2006 against Tampa Bay goaltender Johan Holmqvist, making him the 16th player in NHL history to do so. Power play linemate Brendan Shanahan had scored his 600th goal almost three weeks earlier, making them the first teammates in NHL history to score their 600th goal in the same season.

More injuries struck Jágr in the 2006 Winter Olympics in Turin. He was injured after a hit from Finland’s Jarkko Ruutu, requiring stitches to his eyebrow. However, the injury was not as serious as first anticipated, and Jágr was able to play in the following games, though he was unable to finish the bronze medal game due to muscle injury. Despite the trouble, Jágr won his second-career Olympic medal, the bronze. In 2010, Jágr was his nation’s flag bearer at the 2010 Winter Olympics, but in the men’s ice hockey tournament, the Czechs finished a disappointing seventh after a defeat in the quarterfinals to Finland. Jágr again represented his country at the 2014 Winter Olympics in Sochi, scoring two goals and one assist in five games as the Czech Republic again lost in the quarterfinals.

On 10 February 2007, against Washington, Jágr earned an assist on a goal by Michal Rozsíval to record his 1,500th career point. He is only the 12th NHLer to reach this mark, and the fourth-fastest player to do so after Marcel Dionne, Mario Lemieux and Wayne Gretzky.

On 5 April 2007, against the Montreal Canadiens, Jágr scored his 30th goal of the 2006–07 season to record 15 consecutive seasons of 30 or more goals, tying the NHL record held by Mike Gartner.

On 14 November 2007, against New Jersey, Jágr scored his fourth goal of the 2007–08 season at the Prudential Center in Newark, making him the first player to score a goal in 53 different NHL arenas.

On 3 July 2008, Jágr, an unrestricted free agent for the first time in his career, was informed by Rangers general manager Glen Sather that the club would not offer him a new contract. Sather admitted that the two sides never engaged in detailed negotiations for a new contract, and that after many months of speculation, Jágr was “seriously considering” going to Russia to finish his career, despite offers from other NHL teams. Jágr expressed a desire to possibly finish out his career at his father’s club, HC Kladno. On 4 July, Jágr agreed to a two-year contract with Avangard Omsk of the Kontinental Hockey League (KHL); the contract was reported to pay Jágr the equivalent of US$5 million annually.

When Jágr played in the first game of the 2013 Stanley Cup Finals, he set a new record for the longest gap between Finals appearances at 21 years, surpassing the previous record of 19 years, which was established by Gary Roberts in 2008; coincidentally, both instances involved someone with the Penguins at one end of those streaks. Also coincidental was that, as in his previous Stanley Cup appearance, Jágr’s opponents were the Chicago Blackhawks. After the Bruins lost the Finals to Chicago, the team announced on 26 June 2013 that they did not intend to offer Jágr a new contract.

Jágr was named Avangard’s captain on 30 January 2009. As a member of Avangard, Jágr was sitting next to Alexei Cherepanov, a first-round pick of the New York Rangers, who died during a game against Vityaz Chekhov. They were discussing the past shift when the 19-year-old Cherepanov collapsed onto Jágr on the bench at the Ice Hockey Center 2004 in Chekov.

In April 2009, Jágr publicly stated an interest in returning to the NHL, stating that he really just needed a break from the pressures of an 82-game NHL schedule. Jágr, who claimed to have lost 15 pounds since his last NHL season, and who was “practicing a lot harder than [he] ever did in [his] life”, stated that he would be interested in joining the Edmonton Oilers because of the interest they showed in July 2008. However, following the expiration of his initial contract with Avangard, Jágr signed a new contract with Avangard for the 2010–11 season.

On 26 May 2010, Jágr announced that he was backing the Civic Democrats and its leader Petr Nečas. At the press conference, he said, “I realize that there will be elections in two to three days. I would like their outcome to be good.” He also urged the party not to forget about sports when distributing money. “We all know what would happen if the young did not practice any sport. If children practice some sport, they do not have time for other things such as alcohol.”

On 1 July 2011, Jágr returned to the NHL, but rather than signing with his original NHL team in Pittsburgh, he signed a one-year, $3.3 million contract with the Philadelphia Flyers, the Penguins’ cross-state rival. He scored his 1,600th NHL point during his debut game with the Flyers, assisting on a Claude Giroux goal as the Flyers won their season opener 2–1 over the Boston Bruins on 6 October 2011. Typically playing on the first line with Giroux and Scott Hartnell, Jágr was among the top scorers during the start of the 2011–12 season. He scored his first and second goals as a Flyer on 24 October against the Toronto Maple Leafs. On 29 October 2011, against the Carolina Hurricanes, he scored his 650th and 651st NHL goals. He scored his only goal of the 2012 playoffs during Philadelphia’s series against Pittsburgh. The Flyers were eliminated by the New Jersey Devils, who would ultimately become the 2012 Eastern Conference champions.

On 3 July 2012, Jágr signed a one-year contract with the Dallas Stars reportedly worth $4.5 million. The signing marked Jágr’s first time playing for a club in the Western Conference. Jágr said during a conference call two days later that the Montreal Canadiens had been his first choice as a free agent. “I always wanted to play in Canada and I wanted to go to Montreal if I had a chance, but Montreal wasn’t interested,” Jágr said. “All of a sudden I got a phone call from Stars’ general manager Joe Nieuwendyk that Dallas was interested.”

During the 2012–13 NHL lockout, Jágr played for his own team, Rytíři Kladno, in the Czech Extraliga. During the lockout, he scored 24 goals and 33 assists in 34 games and, before leaving Kladno for the Stars, was in second place of Czech Extraliga’s scoring list. After the NHL lockout ended, he made his debut as a Star on 19 January 2013, when he tallied two goals and two assists in a 4–3 victory over the Phoenix Coyotes.

Jágr reached the 1,000-assist mark on 29 March 2013 in a game against the Minnesota Wild, becoming just the 12th player to do so and the first non-Canadian NHLer to reach the milestone.

On 2 April 2013, Jágr was traded to the Boston Bruins in exchange for Lane MacDermid, Cody Payne and a conditional third-round pick in the 2013 NHL Entry Draft. He made his Bruins debut on 4 April, scoring the lone goal in Boston’s 1–0 win over the New Jersey Devils, and with his second Bruins goal, the first scored in a 3–0 shutout over the Florida Panthers on 21 April 2013, Jágr tied the record for the most game-winning goals in an NHL career (118), previously set by Phil Esposito.

On 22 July 2013, Jágr signed a one-year contract with the New Jersey Devils; the contract included $2 million guaranteed and another $2 million as an incentive bonus if Jágr was to play in at least 40 games. Jágr, at age 41, hoped to help the Devils overcome the loss of Ilya Kovalchuk, who had previously departed for the KHL. Jágr scored his first goal as a Devil on 7 October 2013 in a 5–4 shootout loss to the Edmonton Oilers. The goal came on the 23rd anniversary of his first NHL goal which, coincidentally, was against the Devils.

On 21 November 2013, Jágr tied Gordie Howe’s record of game-winning goals with 121, with his 690th goal, which tied him in ninth place (with former teammate Mario Lemieux) for all-time goal-scoring leaders. On 20 December, he scored his 693rd goal, putting him in eighth place over Steve Yzerman. A day later, Jágr tied Mark Messier for seventh place in NHL history for goals scored with 694. Later in the season, on 14 January 2014, he scored his 695th goal, passing Messier, putting him 14 goals away from passing Mike Gartner. On 1 March, Jágr scored his 700th career NHL goal as the Devils won 6–1 against the New York Islanders at Nassau Veterans Memorial Coliseum. On 8 April, near the conclusion of the Devils’ season, he was awarded the New Jersey Devils MVP Award at their annual team awards ceremony. He scored two points in his final game of the season (two assists in the third period), surpassing Gordie Howe for eighth place on the NHL’s all-time list for career assists and tying Steve Yzerman for sixth on the all-time points list at 1,755. Jágr finished the season as the team’s leading scorer, with his highest points total in a season since 2007–08. Jágr’s play led the Devils to re-sign him to another one-year contract on 30 April. He became the joint sixth-highest scorer in NHL history in November 2014 after scoring his 708th NHL goal for the Devils against Boston. On 8 December, in his 1,500th NHL game, he moved ahead of Marcel Dionne for fifth place on the NHL’s all-time points list with 1,772. On 3 January 2015, in a game against the Philadelphia Flyers, Jágr became the oldest player in NHL history to score a hat-trick at 42 years and 322 days. The record was previously held by Detroit Red Wings defenceman Nicklas Lidström.

After losing to Sweden in a battle for a bronze medal on 2014 IIHF World Championship in Minsk, Jágr announced the end of his career in international play with the Czech national team, focusing his efforts on returning to the NHL playoffs after New Jersey failed to qualify in 2014. However, Jágr stepped back from his decision after being called up to the Czech team for the 2015 IIHF World Championship in Prague and Ostrava, making the team’s roster. On 1 May, he scored a goal in the Czechs’ 6–5 loss to Sweden, his 50th for the national team, to become the oldest player to score at the World Championship. In the Czech Republic’s quarterfinal game against Finland, Jágr scored one assist and two goals, including the game-winning goal. At the end of the tournament, despite the Czechs’ loss in the bronze medal game, Jágr was named the tournament’s most valuable player.

On 26 February 2015, Jágr was traded to the Florida Panthers in exchange for a second-round pick in the 2015 NHL Entry Draft and a third-round pick in 2016. He made his team debut on 28 February in a 5–3 Panthers win over the Buffalo Sabres and registered his first points with the team in the following game on 1 March, posting a goal and an assist in a 4–3 win over the Tampa Bay Lightning. On 19 March, Jágr scored his 718th career goal against Detroit to move him past Phil Esposito and fifth on the all-time goal scoring list. In a 9 April, 4–2 Panthers victory over the Bruins, Jágr registered two assists to give him 1,800 career points in the NHL and sole possession of fourth place on the all-time points list, surpassing former Penguins teammate Ron Francis. On 11 April, in the Panthers’ season finale, Jágr reached 2,000 NHL points (including playoff games) when he assisted on a Jonathan Huberdeau goal. He then scored his 800th NHL goal (including playoffs) later in the third period. On 12 April, one day after the end of the 2014–15 regular season, Jágr signed a new one-year, $3.5 million contract with Florida for the 2015–16 season.

Jágr reached multiple milestones as a Panther. On 20 December 2015, he moved into fourth all-time on the NHL scoring list, scoring his 732nd goal to move past Marcel Dionne for fourth place in NHL history. On 4 February 2016, Jágr became the sixth player in NHL history to record 1,100 career assists. On 20 February, he scored his 742nd goal, surpassing Brett Hull for third place in NHL history. In a 7 March, 5–4 overtime loss to the Bruins, an assist on Aleksander Barkov’s goal put Jágr at 1,851 career points, passing Gordie Howe on the all-time points list and putting him in sole possession of third place overall. With the Panthers qualifying for the 2016 playoffs, Jágr played in his first playoff series since the 2013 Stanley Cup Final. Though he only registered two assists in the Panthers’ six-game first round exit to the Islanders (who would win their first playoff series since 1993), he became the fifth NHL player all-time to record 200 career playoff points.

At age 44, Jágr led the Panthers in scoring with 66 points. In reward for his strong play and leadership abilities, the team announced on 5 May 2016 that they had signed Jágr to a new one-year, $4 million contract.

On 20 October 2016, Jágr became the third player in NHL history to score 750 goals. On 22 December 2016, he scored his 1,888th career point, surpassing Mark Messier to become second in career points, and on 15 February 2017, his 45th birthday, he became the second player to register his 1,900th NHL point.

In 2017 on Twitter, as a free agent, Jágr tweeted: “FA 1994 – all GMs called, FA 2017- 0 calls” accompanied by a trophy emoji and a smiley emoji, as well as pictures taken in 1994 and 2017. In the 1994 picture, a smiling Jágr is on the phone with an unspecified general manager. In the 2017 picture, he is seen looking at his mobile phone with a puzzled expression on his face. The Panthers organization announced shortly after that they would not offer Jágr a new contract.

On 4 October 2017, Jágr signed a one-year contract with the Calgary Flames. Jágr had indicated before that he would like to play professionally until age 50, but later said that it would be very likely that he would stop playing after the 2017–18 season, at which point he would be 46. He noted the tendency of teams to focus on younger players to the exclusion of older ones like himself, which he considers understandable and in light of which he remarked, “I was pretty lucky.” The Flames were Jágr’s ninth NHL team, but his first Canadian team, which prompted him to say, “I want to get the experience so I can one day say I played for a Canadian team. So I’m here.”

On 9 November 2017 against the Detroit Red Wings, Jágr scored his first goal as a Flame, earning two points in a 6–3 win. However, on 6 January 2018, it was reported that Jágr and the Flames were negotiating the termination of his contract, as injuries had limited Jágr to a career-low seven points (including the aforementioned one goal) in 22 games. On 14 January 2018, Jágr was placed on the injured reserve, retroactive to 31 December 2017, while the Flames called up Ryan Lomberg from their American Hockey League (AHL) affiliate, the Stockton Heat, in his place. On 28 January, it was reported that Jágr was placed on waivers, signalling the end of his brief tenure with the Flames; he cleared waivers the following day and was assigned to HC Kladno in the WSM Liga.

On 3 February 2018, Jágr played his first game for his hometown team, and his first game since 31 December 2017, playing nearly 20 minutes and recording three assists. In his fifth game for Kladno, he was injured and remained sidelined for the rest of the season with a knee injury. In order to be eligible for participation in the playoff finals, he played a few seconds in ten playoff games. On 14 May, Jágr announced his plans to remain with Kladno for his 30th professional season. On 19 April, Jágr scored four goals in one game as Kladno was promoted to the top-flight Czech Extraliga.