The younger brother of Sylvain Gagnon, short track speed skater Marc Gagnon began skating at the age of three and, a year later, he was already competing. His World Championship career began in 1993 and he found instant success, winning bronze in the 3,000m event, silver in the 500m competition, gold in the 1,000m contest, and took the overall tournament. He easily made the national team for the 1994 Winter Olympics and took bronze in the 1,000m event, in addition to placing fourth in the 500m competition and the 5,000m relay. Between then and his next Winter Olympics, in 1998, he captured two more World Championship titles in 1994 and 1996, was runner up in 1995 and 1997 tournaments, and took home three more bronze, six more silver, and seven more gold medals. At the 1998 Winter Olympics he captured gold with the 5,000m relay team, but placed fourth in the 500m event once again and sixteenth in the 1000m competition. That year he also won his final overall World Championship, adding four more gold medals to his total. He took 1999 off, but returned in 2000 with a gold medal in the team event at that year’s World Championships. At the 2001 World Championships, his final one, he took gold in the 1,500m event, silver in the 3,000m competition and the 5,000m relay, and third in the tournament overall. His last stop was the 2002 Winter Olympics, where he finally captured gold in the 5,00m event, in addition to winning the 5,000m relay once more and placing third and sixteenth in the 1,500m and 1,000m competitions respectively.
Over the course of his career, Gagnon held many world records. He held the 1,000m record for nearly two years, skating a 1.28,230 on April 4, 1997, a feat that was not surpassed until Fabio Carta skated it in 1.27,424 on January 24, 1999. After skating to a world record 2.18,61 in the 1,500m event on February 6, 1995, he bested his own accomplishment on March 1, 1996 with a time of 2.18,16 and was not surpassed until November 11, 1997. He was a member of a team, which included his brother, Frédéric Blackburn, and Bryce Holbech, that set a world record in the 5,000m relay with a time of 7.09,76 on March 19, 1995 at that year’s World Championships. Replacing Holbech with Derrick Campbell, they improved their record on October 29th of that year to 7.02,48 and held it until December 8, 1996. He retired from active competition after the 2002 Winter Olympics and was inducted into the Canadian Sports Hall of Fame in 2008. He now works as a motivational speaker across Canada.