[10] De Grasse was raised in Markham, Ontario and attended St. Marguerite Bourgeoys Catholic Elementary School from kindergarten to grade two.

[12] He was spotted by future coach Tony Sharpe who noticed his impressive results compensating for the lack of starting blocks and proper racing attire.

[citation needed] All three events were won by his eventual Olympic teammate Bolade Ajomale of Alexander Mackenzie High School.

[citation needed] De Grasse nabbed global attention at the NCAA Championships by winning both the 100 and 200 metres ahead of favourite Trayvon Bromell of Baylor University with wind-aided times of 9.75 and 19.58, respectively.

"[17] After winning the national 100m title with a personal best of 9.95, De Grasse's next major event was the 2015 Pan American Games held in his home province of Ontario.

At the event, De Grasse cruised through his heat in 9.99, then made headlines when he nearly beat Usain Bolt, who stumbled out of the blocks.

"[23] De Grasse also participated in the 4 × 100m relay, where he won a second bronze medal, running a 38.13 together with Aaron Brown, Brendon Rodney, and Justyn Warner.

[citation needed] He impressed many by staying level with Usain Bolt during their semifinal and even appeared to mimic the world record holder, the two Puma sponsorees crossing the line together with smiles.

De Grasse won the bronze medal in the final in 9.91 seconds, a new personal best, behind Bolt and his main rival Justin Gatlin.

Initially in 6th place, De Grasse made an incredible close on Japan and the United States by about 4 metres, though he narrowly missed the bronze medal by 0.02 seconds.

[32][33] After winning both the 100m and 200m national titles, De Grasse was in contention to make the same double in London and defeat the world record holder.

However, just days before the world championships, De Grasse strained his hamstring and was forced to pull out of both events, effectively ending his goal of beating Bolt before his retirement.

[citation needed] A few days later, Bolt also said in an interview that "The last guy I said was going to be great disrespected me", a comment interpreted to be about De Grasse and his unexpected move in the semifinals of the 200 in Rio.

During the 200m heats, he pulled up with a hamstring injury; the crowd cheered De Grasse on as he walked to the finish line, and he ended his season.

Following his injuries, De Grasse left ALTIS and coach Stu McMillan in Arizona, moving to Jacksonville to train under Rana Reider.

[39] Despite initial struggles in the early season, De Grasse appeared to be making a slow return to international competition.

A month later, he won his first Diamond League victory in two years at the Rabat 200m event, beating the reigning World champion Ramil Guliyev.

[citation needed] At the championships, De Grasse made his contention official by winning his semifinal in the 100m, beating defending champion Justin Gatlin and number 2 all-time Yohan Blake.

De Grasse opened his 2021 season on April 17 at the Tom Jones Memorial Invitational in Gainesville, Florida, running the 100m in 9.99.

[44] De Grasse was named to the 2020 Canadian Olympic team and was identified as one of Canada's top medal contenders in athletics, notwithstanding some of his early results that year.

[50] De Grasse then went on to win the gold medal in the 200m final in a personal best and Canadian record time of 19.62 seconds, making him the 8th fastest of all-time over 200 metres.

[51] Hours after his gold medal win, De Grasse competed in the heats of the 4x100 m relay alongside Aaron Brown, Jerome Blake and Brendon Rodney.

"[53] Weeks later in the Diamond League Final in Zürich, De Grasse placed second in both the 100 and 200 metres events, running in both on the same night.

[58] The Canadian team qualified for the finals with the third-fastest time in the heats, De Grasse being pipped at the line by Frenchman Jimmy Vicaut by 0.01 seconds.

De Grasse ran the anchor leg for Canada, maintaining the lead over American Marvin Bracy to secure his first-ever relay major championship gold, breaking the national record he had previously helped set at the Rio Olympics.

"[59] De Grasse was initially named to the Canadian team for the 2022 Commonwealth Games, but withdrew after the World Championships, with Athletics Canada citing a need "to properly recover and prepare for the rest of the season.

"[62] Struggles with injury and the aftermath of COVID continued, and he ended the season with an appearance at the Diamond League Final in Zürich, where he came eighth of eight runners in the 100 m and sixth in the 200 m.[63] Following the conclusion of the 2022 season, with coach Reider under investigation by the U.S. Center for SafeSport for sexual misconduct, De Grasse opted to move to Orlando to train under John Coghlan.

De Grasse explained the move as a family decision based on Jacksonville, Florida being "a much better set-up for our kids with schools and extracurricular activities."

"[83] In the final, the Canadians ran a season's best time of 37.50 and captured the gold medal, in what was widely considered a major upset victory, with a botched baton exchange ending the hopes of the heavily favoured American team.

[90] De Grasse also created and participates annually in a basketball tournament named "Holiday Classic at Markham" at Pan Am Centre.