Ian Millar has competed in more Olympic Games than any Canadian in history, in any sport. He shares the world record for number of Olympic starts with retired Austrian yachtsman Hubert Raudaschl. Both have competed in nine Olympic Games. Millar's ninth Olympic start, in 2008, brought him his first Olympic medal – a team silver, at age 61. It was the first team show jumping medal that Canada had earned in 40 years. Millar is hoping to represent Canada at the 2012 Olympic Games when he will be 65. 

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If Millar's Olympic record is impressive for longevity, his Pan American Games record is equally so for his medal count. He has earned 9 medals in 8 Pan American Games, more than any other show jumper. He earned a team silver and narrowly missed an individual bronze in 2007 in Rio de Janeiro. He has twice been the Pan American Games individual gold medalist (1987 and 1999).

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In spite of his Olympic and Pan American Games records, it was the World Cup of show jumping where Millar first broke new ground. In 1988 and '89 he and his legendary partner, Big Ben, became the first-ever rider and horse combination to win back-to-back World Cup Finals. He has represented Canada in fourteen World Cup Finals and recorded five top-eight finishes.

Millar has represented Canada at six World Championships, where he has been a member of three top-five-placed teams and has finished in the top-ten individually twice.

He is a ten-time Canadian Champion, having last won the title in 2007. That national championship made Canadian show jumping history, as Millar and his son, Jonathon, logged a 1-2 finish in a close battle for the title.

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Millar is the most decorated equestrian in Canadian history. He was awarded the Order of Canada in 1986 and was Ontario's Athlete of the Year in 1989. In 1996, he and Big Ben were both inducted into the Canadian Sports Hall of Fame. Big Ben was only the second horse to receive this honour, the first being Northern Dancer. Millar was awarded an honorary doctorate by the University of Guelph, Ontario, in 2005.

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Millar works closely with his son, Jonathon, and daughter, Amy, who are both successful riders in national and international grand prix. They operate Millar Brooke Farm together and have been dubbed "Team Millar".