Hamelin's early success at the 2003 World Junior Championships saw him win silver medals in the 500 m and the 1500 m races and a bronze in the 5000 m relay.

In his first Olympics, he finished in fourth place in the 1500 m and won a silver medal as part of the Canadian relay team.

[3][4] Hamelin made his debut at the world junior championships in 2002, finishing fourth in the 500 m and helping the relay team to a silver medal.

He was seemingly following the footsteps of a long line of accomplished French-Canadian short track speedskaters like Marc Gagnon and Éric Bédard.

Going into the 2004 World Championships, the Canadian men's relay team was considered one of the favourites but only managed a fourth-place finish.

For three-quarters of the race, he stood in first position in front of François Hamelin and Apolo Ohno, only to be surpassed by Korea's Lee Ho-Suk in the sixth lap.

[11] During the race the crowd at the Pacific Coliseum was cheering so loudly during the 1,000 m final that Hamelin felt an overwhelming sense of pride like never before, calling it "amazing."

Despite the crowd support, Hamelin remained disappointed as he had gone to the Olympics with a mind to win multiple medals.

It was a close race as the world record holder, Korea's Sung Si-Bak, was in the lead until a slip in the final corner, which allowed Hamelin to pass to finish first.

[16] Hamelin put up decent results through the 2012 season despite several nagging injuries and carried that success into the World Championships.

Hamelin was injured in the fall and did not compete in the men's relay final, but he still won gold for his earlier participation in the semi-final.

Towards the end of the race, Hamelin's lead was challenged by both China's Han Tianyu and Russia's Viktor Ahn, but Hamelin passed Han and held on to win the gold medal as Canada's second gold medal of the Sochi Olympics.

[3] He rebounded from the disappointing Olympics to win his first ever World Championship overall title, taking gold in the 1000 m and 1500 m events and silver in the men's relay on home ice in Montreal, after several near misses previously.

[21] Hamelin had been widely expected to retire following the 2017–18 season but surprised many by announcing that he intended to continue for at least another year.

[22][3] The onset of the COVID-19 pandemic resulted in the cancellation of many events in the second half of the quadrennial and greatly complicated Hamelin's training.

[24][25][26] As well, Hamelin along with hockey player Marie-Philip Poulin were named as Canada's flagbearers during the opening ceremony.

He was disqualified for an illegal lane change in the semi-final, while teammate Steven Dubois won the silver medal.

[3] Following the Olympics, the 2022 World Championships, held in Montreal, were expected to be the final event of Hamelin's competitive career.

Canada's 50 most beautiful Canadians list in 2010, along with his then-girlfriend, fellow speed skater and Olympian Marianne St-Gelais.

[36] He is presently engaged to sports journalist Geneviève Tardif, with whom he shares a daughter, Violette, born on April 23, 2020.