Born in Toronto, Ontario, Simmons first began training at the Toronto Newsboys Boxing Club in Toronto, Ontario in 1979. He was a member of the Canadian National Boxing Team travelling to over 20 countries from 1993 to 2000. In 1996, Simmons was the Canadian Olympic alternate in the 91 kg weight division to David Defiagbon (1996 Atlanta, Olympics, Silver medalist). In 1995, Simmons won the Detroit Golden Gloves in the 91 kg Heavyweight division when Canadians were still allowed to compete at the US Golden Glove Championships. He would then represent Detroit competing at the 1995 National Golden Gloves in Lowell, Mass winning his first two bouts, losing in the quarter-finals. At the 1997 World Championships in Budapest, Hungary, he defeated Macedonia via a first round knock out, then won a decision on points 18-10 over USA's Davaryll Williamson and lost in the quarter-finals on points, 14-10 to Cuba's Félix Savón, who has been regarded as one of the world's greatest amateur boxers. In 1997, AIBA ranked Mark Simmons fifth best boxer in the 91kg division in the world. In 1997, Simmons won a silver medal at the Francophone games in Antananarivo, Madagascar with a first round knock out over Madagascar in the first fight, a second-round decision victory over France and a 14-15 loss to Cameroon in the final. At the 1998 Commonwealth Games in Kuala Lumpur, Malaysia, Simmons won the gold medal in the 91 kg heavyweight division with victories over Ghana, Wales, and the Seychelles. At the 1999 Pan American Games in Winnipeg, Manitoba, Simmons defeated Jamaica in the quarter-finals, USA in the semi-final, and lost to Odlanier Solís of Cuba in the final by a 4-2 score in the taking home the silver medal, despite boxing with a broken hand. as a result of his broken hand, Simmons was unable to participate in the 1999 World Championships that took place two weeks after the Pan Am Games.