On September 21, Halladay became the first Phillies pitcher to win 20 games in a season since Steve Carlton accomplished it in 1982. He was the first right-handed Phillies pitcher to accomplish the feat since Robin Roberts in 1955. One week later, on September 27, he completed his 21st victory, helping the Phillies clinch their fourth consecutive National League East title, and the Phillies finished with the best regular season record in MLB.

Halladay was named by his peers as the Players Choice Awards NL Outstanding Pitcher. He was also unanimously chosen as the recipient of the 2010 National League Cy Young Award, becoming the first Phillie to win the award since Steve Bedrosian in 1987 and only the fifth pitcher in MLB history to win the award in both leagues, joining Gaylord Perry, Pedro Martínez, Randy Johnson and Roger Clemens. He was likewise selected as the Sporting News NL Pitcher of the Year, the USA Today NL Cy Young, the Baseball Prospectus Internet Baseball Awards NL Cy Young, and the winner of the NLBM Wilbur “Bullet” Rogan Legacy Award (NL Pitcher of the Year). He also was named the MLB “This Year in Baseball Awards” Starting Pitcher of the Year. Baseball Digest named him its Pitcher of the Year (including both leagues). Baseball America named him its Major League Player of the Year (including all positions in both leagues). MLB named him its “MLB Clutch Performer of the Year”. He was given the Heart & Hustle Award by the Major League Baseball Players Alumni Association. He was also named Pro Athlete of the Year by both the Sporting News and the Philadelphia Sports Writers Association and Sportsperson of the Year by the Philadelphia Daily News. The Philadelphia chapter of the Baseball Writers’ Association of America presented him with the “Steve Carlton Most Valuable Pitcher” and “Dallas Green Special Achievement” awards.

Halladay attended Arvada West High School, where he led the school’s baseball team to a 6A state championship in 1994. In 1995, after graduating from high school, he was selected by the Toronto Blue Jays in the amateur draft, in the first round, as the 17th overall pick. Halladay decided to forego his college baseball commitment to Arizona and sign with Toronto. He was promoted to the major-league club as a September call-up in 1998.

In his second career start, against the Detroit Tigers on September 27, 1998, Halladay had what would have been the third no-hitter ever pitched on the final day of a regular season broken up with two outs in the ninth. The feat would have joined the combined no-hitter by four Oakland Athletics pitchers (Vida Blue, Glenn Abbott, Paul Lindblad, and Rollie Fingers) in 1975 and Mike Witt’s perfect game in 1984. The bid was broken up by pinch hitter Bobby Higginson’s solo home run, the only hit allowed in a 2–1 Toronto victory, as he recorded his first major league win. Prior to the home run, the sole base runner had reached on an infield error in the fifth inning, as Halladay struck out eight and walked none.

During the 2000 season, Halladay sported a 10.64 earned run average (ERA) in 19 games, 13 of which he started, making his 2000 season the worst in history for any pitcher with at least fifty innings pitched. At the beginning of the 2001 season, Halladay was optioned to Class A Dunedin to rebuild his delivery.

Halladay’s fastball was clocked up to 95 mph (153 km/h), but it had little movement, and his pitches were up in the strike zone, which was ultimately the reason why his 2000 season was so unsuccessful. He worked with former Blue Jays pitching coach Mel Queen. The problem, Queen realized, was Halladay’s total reliance on his strength—his attempt to overpower batters with straight-ahead pitches. Within two weeks, Halladay had altered his arm angle for a more deceptive delivery, and added pitches that sank and careened. Instead of throwing over the top, he chose to use a three-quarters delivery (the middle point between throwing overhand and sidearm). Originally a fastball pitcher, he became reliant on keeping his pitches low across the plate, regardless of the type of pitch thrown. The adjustments proved successful. After a month and a half, he was promoted to Double-A Tennessee, and a month later, to Triple-A Syracuse. By mid-season, he was back in the Blue Jays’ rotation. He posted a 5–3 win–loss record with a 3.19 ERA for the Blue Jays in 16 starts in 2001.

In 2001, after being demoted to the minor leagues, Halladay immersed himself in the works of sports psychologist Harvey Dorfman. This exposure was at least partly responsible for resurrecting his career. In 2002, Halladay had a breakout season, finishing with a 19–7 record, while posting a 2.93 ERA with 168 strikeouts in 239.1 innings. Halladay was named to the American League All-Star team.

Halladay continued his success in the 2003 season, posting a 22–7 record with a 3.25 ERA in 266 innings. He also recorded 204 strikeouts and only 32 walks, good for a 6.38 strikeout-to-walk ratio. Halladay pitched the first extra-inning shutout in the major leagues since Jack Morris in Game 7 of the 1991 World Series, leading the Blue Jays to victory over the Tigers on September 6. He pitched 10 innings and had not allowed a hit until Kevin Witt doubled with two outs in the top of the eighth. Halladay won the American League Cy Young Award, while being once again named an All-Star and leading the Blue Jays to a surprising 86 victories. He was named by his peers as the Players Choice Awards AL Outstanding Pitcher. He was also named the Sporting News AL Pitcher of the Year and the Baseball Prospectus Internet Baseball Awards AL Cy Young Award winner.

In 2004, Halladay was placed on the disabled list twice due to right shoulder problems. In 133.0 innings, he went 8–8 with a 4.20 ERA. He walked 39 batters, seven more than he had walked in 2003 when he had pitched twice as many innings. He later revealed that he had been injured throughout the entire season with a “tired throwing arm”, which he believed was from intense workouts in preseason.

The 2005 season began successfully for Halladay, as he posted a 12–4 record with a 2.41 ERA in 19 starts. He was selected to his third All-Star team and was slated to be the starting pitcher for the American League at the All-Star Game in Detroit. However, on July 8, Halladay’s leg was broken by a line drive off the bat of Texas Rangers left fielder Kevin Mench. As a result, he was replaced in the All-Star Game by Matt Clement of the Boston Red Sox, while Mark Buehrle of the Chicago White Sox was named the starting pitcher for the American League. Despite rehabilitation of his leg, Halladay would sit out the remainder of the season.

On March 16, 2006, Halladay signed a $40 million three-year contract extension through 2010. During that year, Halladay finished near the top of the MLB in wins with 16. He was named to the American League All-Star Team as a reserve on July 3, along with four of his Blue Jays teammates. It marked the second-most appearances in club history, and Halladay’s fourth as an All-Star. Although Halladay’s strikeout total was lower in 2006 than in previous seasons, his ground ball/fly ball ratio, complete games, and innings pitched were all among the American League leaders.

Halladay was the American League pitcher of the month in April 2007, going 4–0, highlighted by a 10-inning complete game win over the Detroit Tigers. However, he pitched poorly in his two starts in May, and on May 11 was placed on the disabled list and underwent an appendectomy. He returned to the rotation in his usual form on May 31 against the Chicago White Sox. Halladay went 7 innings, giving up just six hits and allowing no runs on his way to his 100th career win. 2007 also saw Halladay hit his first career RBI. Against the Los Angeles Dodgers on June 10, his ground ball single to center field allowed John McDonald to score. He shut out the Seattle Mariners on July 22, allowing only three hits.

Halladay’s distinctiveness was characterized by his ability to throw a hard two-seam sinking fastball ranging in the low 90s with pinpoint control. In addition, he threw a four-seam fastball in the low 90s, a curveball in the high 70s, and cut fastball from 90 to 92 mph for which he had modified his grip in 2007 at the suggestion of former catcher Sal Fasano. Halladay threw the hardest cutter among MLB starters in the 2011 season, at an average of 91.4 mph. The changeup was one pitch that Halladay had problems commanding for many years, and which he used very rarely. However, after joining the Phillies in 2010, Halladay started throwing a changeup that was a variation of the split-finger fastball (called a split-changeup). The pitch was introduced to Halladay by pitching coach Rich Dubee.

In 2008, for the sixth consecutive year, Halladay was Toronto’s opening-day starter, improving his own club record. He lost 3–2 in a pitcher’s duel with New York’s Chien-Ming Wang. His first win of the season came in his next start against Boston, when he outpitched Josh Beckett in his season debut.

In his third start, Halladay pitched a complete game against the Texas Rangers, in a 4–1 win. Three of his nine complete game efforts resulted in losses due to Toronto’s underachieving offense early in the season. In fact, those three complete game losses came in three consecutive starts. On June 20 against the Pittsburgh Pirates, he was struck in the temple by a line-drive off the bat of Nyjer Morgan. The ball caromed off Halladay’s head and was caught by third baseman Scott Rolen, ending the inning. Halladay was able to walk back to the dugout, but was taken out of the game for safety concerns. Although he was given a clean bill of health for his next start, it was later suggested by television commentators that Halladay may have in fact suffered a temporary lapse in recognition of what happened on the play. Halladay pitched his 10th career shutout against the Seattle Mariners on June 30. He limited them to four hits in his sixth complete game of the season. The shutout tied him with the Cardinals’ Mark Mulder for 10th among active pitchers. On July 11, 2008, Halladay pitched his 7th complete game and second shutout of the season against the New York Yankees, allowing 0 runs on 2 hits for his 38th career complete game. Halladay was named to the American League All-Star Team as a reserve. He pitched in the fourth inning, yielding only one hit and striking out Lance Berkman. In his last start of the season, he fittingly pitched a complete game against the Yankees to win his 20th game of the year. In so doing, he became the first pitcher to win five games against the Yankees in a single season since Luis Tiant in 1974. In addition, he led the AL with a 1.05 WHIP. Halladay finished second in the American League Cy Young Award voting, behind Cliff Lee of Cleveland. He also led the AL with 9 complete games, and struck out a career-high 206 batters (two more than his 2003 season) as well as posting a 2.78 ERA (the second-best of his career) that was second only to Cliff Lee’s 2.54 ERA. Halladay also became just the fourth pitcher in major league history to post two seasons of 200 strikeouts and fewer than 40 walks. He was presented the George Gross/Toronto Sun Sportsperson of the Year award.

Halladay was the Blue Jays’ nominee numerous times for the Roberto Clemente Award for his work with underprivileged children. For the same reason, he was also the Blue Jays’ nominee in 2008 for the Players Choice Awards Marvin Miller Man of the Year Award.

On April 6, 2009, Halladay made his team-record seventh straight Opening Day start for Toronto, defeating the Detroit Tigers. Halladay then also won his next two starts, on the road against Cleveland and Minnesota. Halladay lost his next game to Texas, giving up 5 earned runs over 8 innings only to go on and win his next 6 games to bring his record up to 8–1 with a 2.75 ERA. With season-ending injuries to planned 2009 Jays’ starters Dustin McGowan and Shawn Marcum, and with #2 starter Jesse Litsch on the disabled list early in the season, Halladay led a staff of young, mostly inexperienced starters. Halladay was named the AL Player of the Week for the period ending May 17. Doc was 2–0 with a 1.13 ERA over 16.0 innings in his two starts the week prior. In a game against the Los Angeles Angels of Anaheim on June 2, Halladay struck out 14 batters and threw 133 pitches, both career highs. On June 12, he left the game early because of a strained hip adductor muscle, commonly referred to as a pulled groin, and was placed on the 15-day disabled list on June 17. On July 5, he was selected to represent Toronto at the All-Star Game. On July 14, he started the All-Star Game for the American League, pitching 2 innings and giving up 3 runs, of which 1 was unearned. That year, he was named #7 on the Sporting News’s list of the 50 greatest current players in baseball. A panel of 100 baseball people, many of them members of the Baseball Hall of Fame and winners of major baseball awards, was polled to arrive at the list.

As of the conclusion of his start on September 20, 2009, Halladay was tied for the second-longest streak in the American League that season with a 24-inning scoreless streak. Halladay finished the season with a 17–10 record, giving him a career win percentage of .660, good enough for 18th all-time. In December, Sports Illustrated named Halladay as one of the five pitchers in the starting rotation of its MLB All-Decade Team.

On December 15, 2009, the Blue Jays traded Halladay to the Philadelphia Phillies for minor league prospects Travis d’Arnaud, Kyle Drabek, and Michael Taylor. He agreed to a contract extension worth US$60 million that included a US$20 million vesting option for a fourth season. Phillies general manager Ruben Amaro, Jr. had unsuccessfully attempted to get Halladay at the non-waiver trade deadline in July 2009, then traded for Cliff Lee instead. Three hours before Halladay signed the contract extension, Amaro traded away Lee, to the surprise of Halladay who thought that Lee would be his teammate.

Halladay pitched his first shutout in the National League, against the Atlanta Braves on April 21, becoming the first pitcher to reach four wins in the 2010 season. On May 1, Halladay pitched his second shutout of the season, limiting the New York Mets to three hits and striking out six.

On May 29, 2010, Halladay pitched the 20th perfect game in MLB history against the Florida Marlins in Miami, retiring all 27 batters and striking out 11, allowing no hits, runs, walks, or errors. This was the first time in the modern era that two pitchers (Dallas Braden of the Oakland A’s and Halladay) had thrown perfect games in the same month and that multiple perfect games had been achieved in the same season. When Halladay’s former manager, Cito Gaston, called to congratulate him, Halladay was unable to take the call because he was busy with the post-game media frenzy.

On August 24, 2010, to commemorate his perfect game, Halladay presented around 60 Swiss-made Baume and Mercier watches he had purchased to everyone in the clubhouse. The watches were presented in brown boxes that bore the inscription: “We did it together. Thanks, Roy Halladay.” Additionally, the back of each watch was engraved with the date of the game, the line score, and the individual recipient’s name.

On October 6, 2010, in his first postseason appearance, Halladay pitched a no-hitter (his second of the season), against the Cincinnati Reds in the first game of the National League Division Series (NLDS).

In May, Halladay was named the 2011 winner of the John Wanamaker Athletic Award, by the Philadelphia Sports Congress, based on his 2010 season. In June, Halladay was presented the Best Major League Baseball Player ESPY Award, for his performance since June 2010.

For the 2011 season, Halladay was joined by Cliff Lee, who before the 2010 season had been traded away from the Phillies shortly before Halladay joined. The resulting starting pitching lineup of Halladay, Lee, Cole Hamels, Roy Oswalt and Joe Blanton had commentators dub it one of the best rotations ever assembled. Halladay, Oswalt, Lee, and Hamels were dubbed the ‘Phantastic Phour’ by fans and the media.

On April 24, 2011, Halladay struck out 14 and allowed just 5 hits in the game as his team swept the San Diego Padres in all four games. Halladay took a two-hitter into the ninth before allowing three straight singles. He allowed just one run and won, 3–1.

On July 12, Halladay was the NL starting pitcher in the All-Star Game. Halladay went 19–6 in 2011, with a 2.35 ERA, and pitched 8 complete games, second most in the Majors. The Phillies won their fifth consecutive National League East championship, and also finished with the best record in baseball for the second straight year.

On April 5, 2012, Halladay threw 8 innings of shutout ball against the Pittsburgh Pirates on Opening Day, giving up 2 hits while striking out 5.

After struggling in spring training, Halladay gave up five runs in his first start in the Phillies second game on April 3, 2013, striking out nine in 3⁄3 innings pitched. After struggling in his prior starts, Halladay pitched eight innings allowing just one run on April 14, 2013, against the Miami Marlins whom the Phillies defeated 2–1. Halladay recorded his 200th career win in the game.

On December 9, 2013, Halladay signed a ceremonial one-day contract with the Blue Jays and announced his retirement from baseball due to injury. At his press conference, Halladay listed a persistent back injury, as well as wanting to be more involved with his family, as his reasons for retiring.

Although retired as a player, Halladay continued to be a part of the game as a guest instructor for the Philadelphia Phillies and Toronto Blue Jays. The Phillies hired Halladay as a “mental skills coach” in March 2017. Halladay also volunteered as a baseball coach at Calvary Christian High School in Clearwater, Florida where his oldest son played baseball.

On November 7, 2017, Halladay died when the ICON A5 Founders Edition amphibious aircraft he was piloting crashed into the Gulf of Mexico. The Pasco County, Florida, Sheriff’s Office confirmed that Halladay was the only occupant of the aircraft at the time of the crash and that air traffic controllers had not received any mayday distress signals from the plane before the crash. The crash was reported to have happened about 0.25 mi (0.40 km) off the coast of New Port Richey, Florida, in water 4 feet (1.22 m) deep.

In late 2017, the Phillies announced that use of uniform number 34 would be suspended for the 2018 season to honor Halladay. On February 12, 2018, the Toronto Blue Jays announced they would retire Halladay’s number 32 on Opening Day of the 2018 season.

Halladay was elected to the Canadian Baseball Hall of Fame in 2017 and the Baseball Hall of Fame and Museum on January 22, 2019 in his first year of eligibility, garnering 85.41% of the vote. His wife and sons announced that they did not choose a logo for his cap, which leaves Roberto Alomar as the sole Cooperstown inductee as a Blue Jay. However, Halladay had said that, if given the choice, he would be inducted as a Blue Jay.

Halladay had two children, Braden and Ryan, with his wife, Brandy (née Gates). During the offseason, Halladay lived with his family in Tarpon Springs, Florida. Halladay’s older son, Braden, committed to play baseball at Penn State shortly after Halladay’s death. Braden, who was born in Toronto, was invited to Baseball Canada’s U18 spring training camp on March 6, 2018, and pitched a scoreless inning in the Canadian Junior team’s exhibition game against the Blue Jays on March 17. In the 2019 MLB draft, as a tribute to Halladay, Braden was selected by the Blue Jays in the 32nd round.

An autopsy report by the Pinellas-Pasco Medical Examiner’s Office released in January 2018 revealed that Halladay’s blood contained morphine, hydromorphone, amphetamine, fluoxetine (an antidepressant), baclofen (a muscle relaxant), and zolpidem (a sleep aid sold under the brand name Ambien). According to forensic pathologist Burr Hartman, “He had a drug combination similar to a speedball. He was impaired by these drugs. It was definitely not safe for him to fly an airplane.” On April 15, 2020, the National Transportation Safety Board (NTSB) released a report stating that in addition to the drugs, Halladay was executing aerobatics including steep climbs and turns, and the plane sometimes came within 5 feet (1.5 m) of the water before a final climb caused its speed to fall to 85 mph (137 km/h), after which it nosedived into the sea and Halladay was killed by blunt force trauma and drowning. The NTSB determined the probable cause of the crash to be the “pilot’s improper decision to perform aggressive, low-altitude maneuvers due to his impairment from the use of multiple psychoactive substances, which resulted in a loss of control”.

On March 2, 2019, Phillies free agent acquisition Bryce Harper, who wore uniform number 34 from his debut with the Washington Nationals in 2012, announced that he would not wear the number 34 as a member of the Phillies, stating that “Roy Halladay should be the last one to wear it” for the Phillies. Harper chose to wear number 3 instead.

On February 4, 2020, the Phillies announced they would retire Halladay’s number 34 on May 29, 2020, the 10th anniversary of his perfect game. However, due to the COVID-19 pandemic, the number retirement was postponed.