Hazard is a Belgian youth international and has represented his nation at under-16, under-17, and under-18 level. With the under-16 team, Hazard was a regular participant. He made his debut on 16 September 2008 in a 5–0 defeat to Germany in a tournament in Hassloch. In the team’s next match in the tournament, against Macedonia, Hazard scored a goal in a 3–0 victory. For the rest of the under-16 campaign, he scored goals in matches against Malta and Poland. Hazard also played with the team at the 2009 edition of the Aegean Cup in Turkey. He featured in all three matches as Belgium crashed out in the group stage portion of the competition.

Hazard grew up in Braine-le-Comte, a small town in the Wallonia region, but he was born in La Louvière. His first name was inspired by the Belgian comic strip Thorgal and he grew up in a family where football was dominant. His mother Carine and father Thierry were both footballers in Belgium. His father spent most of his career playing at semi-professional level with Louviéroise in the Belgian Second Division. He played mainly as a defensive midfielder. His mother played as a striker in the Belgian Women’s First Division and stopped playing when she was three months pregnant with his older brother Eden. After playing football, both parents became physical education teachers. Thierry retired from his position in 2009 in order to devote more time to his children.

Due to his increased participation with Lens domestically, Hazard primarily played in competitive matches with the under-17 team under coach Bob Browaeys. In August 2009, he played with the team in the Toto Cup, a yearly international youth tournament held in Austria. In the first qualifying round for the 2009 UEFA European Under-17 Championship, Hazard scored his only goal with the team in a 1–1 draw with Montenegro. He was subsequently called up to the team in March 2010 for Elite Round qualification matches that were played in Northern Ireland. Hazard played in all three matches as Belgium failed to earn qualification to the tournament.

On 7 April 2010, Hazard signed his first professional contract after agreeing to a three-year deal until June 2013. Ahead of the 2010–11 season, Hazard trained with the senior team during the pre-season. On his pre-season debut, he scored a goal in a 1–1 draw with Belgian club Roeselare. However, Hazard began the season with the club’s Championnat de France amateur team in the fourth division. He made his amateur debut on 8 August 2010, appearing as a substitute in a 2–0 victory over Drancy. After spending most of the season playing concurrently with the reserve team in the CFA and with the under-19 team in the Coupe Gambardella, on 9 May 2011, Hazard was named to the senior team for the first time on 11 May in a Ligue 1 match against Bordeaux. However, Hazard did not feature in the match and finished the 2010–11 campaign with no senior team appearances.

Hazard appeared in only one match with the under-18 team before bypassing the age level to represent the under-19 team ahead of the 2011 UEFA European Under-19 Championship. He made his debut on 8 February in a friendly match against Belarus, scoring the team’s only goal in a 1–0 win. On 27 March 2011, Hazard scored the game-winning goal converting a penalty in a 2–1 win over Ukraine. In Elite Round qualification for the 2011 UEFA European Under-19 Championship, Hazard featured as a starter and played the entire match in all three group stage matches. In the second group stage match against Estonia, Hazard netted the winner in the 88th minute to give Belgium a 3–2 win. The victory allowed the nation to qualify for the tournament with one match to spare. Belgium ultimately finished the Elite Round unbeaten.

At the 2011 UEFA European Under-19 Championship, Hazard featured in two of the three group stage matches Belgium contested. In the team’s opening match against Spain, Hazard assisted on the team’s only goal in a 4–1 defeat after his shot from distance was blocked by the Spanish defence and fell into the path of teammate Florent Cuvelier, who converted his shot. Belgium ultimately finished last in its group, which resulted in the team being eliminated from the tournament.

Due to being an underage player in the 2010–11 season, Hazard remained eligible to play on the under-19 team for the 2011–12 season. In the first match of the campaign against Denmark, Hazard scored the team’s only goal converting a penalty in a 1–1 draw. On 7 September 2011, he scored the second goal in the team’s 4–1 friendly match win over Turkey. In first round qualification for the 2012 UEFA European Under-19 Championship, Hazard scored a team-leading three goals. In the first group match against Wales, he scored a double in a 3–0 win and, in the team’s final group match against Scotland, Hazard netted the second goal in a 3–1 victory. In Elite Round qualification, Hazard appeared in two of the team’s three group stage matches as Belgium finished third in the group behind favourites Spain and Italy.

On 24 July 2012, Chelsea confirmed on its website the club had agreed terms with Lens for the transfer of Hazard, soon after the signing of his brother Eden from Lille. He made his debut on 17 August 2012 in an Under-21 Premier League match, a 0–0 home draw against Manchester City in what was to be his only appearance in Chelsea colours before leaving the club.

On 30 August 2012, Hazard was sent on a season-long loan move to Belgian Pro League club Zulte Waregem. The move was set up to allow him first-team experience rather than be developed slowly by Chelsea.

On 30 August 2012, Hazard was loaned out to Zulte Waregem until May 2013. He made his debut on 15 September 2012 in a 1–0 away win against OH Leuven. Hazard scored his first goal on 31 October in a 4–1 home win against Charleroi. On 16 May 2013, Hazard put in an impressive shift as he scored the game’s opening goal from the penalty spot before providing two assists in a 5–2 defeat of Club Brugge at the Regenboogstadion in Waregem.

Hazard has three other siblings. His older brother, Eden, played for Lens’ biggest rivals Lille and now plays for Real Madrid in Spain. Hazard’s other younger brothers are Kylian and Ethan. In 2013, Kylian joined White Star Bruxelles, and on 29 August 2017, he signed to join Chelsea’s development team, however is currently playing for Cercle Brugge. Ethan goes to the youth academy of Eden’s former club, Tubize. Hazard and his three brothers were raised in a comfortable environment with their parents ensuring they had whatever they needed to excel. The family lived “no more than three meters” from a football training ground and the brothers often ventured onto a training pitch through a small hole in order to hone and develop their skills.

On 15 July 2013, Chelsea and Waregem agreed for Hazard to be loaned back for another year until the end of the 2013–14 season. Hazard scored a free-kick and assisted a goal as Zulte won their season opener against Lierse on 27 July.

On 28 November 2013, Hazard scored against Wigan Athletic in a 2–1 win in the UEFA Europa League group stage win away at the DW Stadium. He was voted as Zulte’s player of the season, and scored 17 goals in 53 matches across all competitions. Hazard also won the Belgian Player of the Year Award.

On 16 May 2013, Hazard earned his first senior call-up after being included in Marc Wilmots’ 28-man squad ahead of a friendly with the United States followed by a 2014 FIFA World Cup qualifier against Serbia. On 29 May, he made his senior international debut for Belgium as a second-half substitute for Chelsea teammate Romelu Lukaku in the 4–2 friendly win over the United States. Hazard was one of seven standby players named for Belgium’s squad for the 2014 World Cup final stages. It took him three-and-a-half years to gain his second cap, in a 1–1 Low Countries derby friendly away to the Netherlands on 9 November 2016, again from the bench.

On 5 July 2014, Hazard was loaned to Borussia Mönchengladbach of the German Bundesliga for the 2014–15 season. During his loan, Hazard wore the number 26. In the 3–1 win against FC 08 Homburg in the DFB-Pokal 16 August 2014, Hazard made his debut, coming on in the 78th minute as a substitute for Branimir Hrgota. He then made his league debut 24 August 2014 in a 1–1 draw against VfB Stuttgart, coming off the bench in the 67th minute.

Hazard scored twice in Gladbach’s 7–0 win over FK Sarajevo in the UEFA Europa League play-offs on 28 August 2014, including a curling free-kick from 35 yards out. On 24 September 2014, Hazard made his first start for Borussia Mönchengladbach in the Bundesliga, against Hamburger SV, playing 71 minutes before being substituted for Fabian Johnson in a 1–0 win. On 6 December 2014, Hazard started against Hertha BSC, only his second start in the Bundesliga. He played the full 90 minutes and assisted Tony Jantschke for the first goal of the match in the opening ten minutes, as well as scoring the winning goal in the 83rd minute, his first of the Bundesliga season. The match ended in a 3–2 win, breaking the club’s four-match winless streak.

On 23 February 2015, Hazard agreed to sign permanently for Borussia Monchengladbach, affective from 1 July. He joined on a five-year contract, thus lasting until June 2020, a buy-back agreement with Chelsea was also included. The contract consists of four years, along with one year optional. The transfer fee was reported as €8 million (£5.9 million), 16 times as much as Chelsea paid for him. During an interview about his move becoming permanent in the summer, Hazard confirmed his deal does contain a buy-back clause and that he still dreams of returning to Stamford Bridge in the future. In his interview, he said, “I am focusing on excelling at Borussia Monchengladbach, but I still hope to play for Chelsea one day.”

On 8 August 2015, in his first game after his transfer, Hazard scored in a 4–1 win at FC St. Pauli in the first round of the DFB-Pokal. Following the resignation of manager Lucien Favre, who lost the first five matches of the Bundesliga, and André Schubert’s appointment, he was unable to find a place in the starting lineup. Hazard made his first start under Schubert on 20 December against Darmstadt 98, eventually earning preference from Schubert over Ibrahima Traoré on the right side. Hazard finished the season with four goals, two coming in a match against Hertha BSC on 3 April 2016 in a 5–0 win.

Looking to improve his playing time and goalscoring heading into the year, Hazard scored his first ever hat-trick in a 6–1 victory over Swiss club Young Boys in the second leg of the UEFA Champions League play-off round on 24 August 2016. Mönchengladbach set a record with a 9–2 aggregate scoreline, the largest ever margin of victory in a play-off tie. On 17 September, Hazard and teammate Raffael both scored first-half braces against Werder Bremen in a Bundesliga match.

On 25 November 2017, he scored from the penalty spot to help his side defeat the Bundesliga record champion Bayern Munich with a 2–1 win. Hazard also scored twice in a 2–1 victory against Hertha BSC, and ended the season with eleven goals and six assists.

On 19 August 2018, Hazard, Alassane Pléa and Raffael each scored hat-tricks in an 11–1 win at fifth-tier BSC Hastedt in the first round of the cup.

Hazard scored his first goal in a 2018 FIFA World Cup qualifier on 10 October 2017 in a 4–0 home victory against Cyprus. On 4 June 2018, manager Roberto Martínez named Hazard in Belgium’s 23-man squad for the 2018 FIFA World Cup in Russia. He made his tournament debut on 18 June, playing the last seven minutes of the group match against Panama in place of Dries Mertens in a 3–0 victory, and played the entirety of the 1–0 win against England in the next match in Kaliningrad; the Belgians finished in a best-ever third place.

On 22 May 2019, Hazard joined Borussia Dortmund on a five-year contract for a reported fee of €25.5 million. He joined the club at the same time as new teammate Julian Brandt, who arrived from Bayer 04 Leverkusen.