Gillis skied until competitively until the age of 15 when he decided to concentrate on dancing, only the dancing he did was on sheets of ice in the QMJHL.
A star with the Sherbrooke Beavers. He scored 140 points in his final year of junior, and was named to the all star team and led the team to Memorial Cup finals. He also starred at the then-unofficial world junior hockey championships, helping Team Canada capture the silver medal.
With his amateur career complete, the Vancouver Canucks chose Gillis 4th overall in the 1977 Entry Draft. He would go on to play 400 NHL games in the 1970s and 1980s. He was a decent two-way player but more was expected of him after his stellar junior career.
Gillis enjoyed a fine rookie season in 1977-78 with 23 goals while playing on a line with Mike Walton and Rick Blight. He was unable to build on his strong freshman performance and turned in consecutive 13-goal performances before he was traded to the New York Rangers. Over the next several years he was a utility player with the Blueshirts, Quebec Nordiques, Buffalo Sabres, the Canucks a second time, and the Philadelphia Flyers.
Gillis' time in Buffalo was very brief. He played just 3 games in the 1982-83 season. Otherwise he was a valuable presence on the Sabres farm team that season, guiding the AHL Rochester Americans to the Calder Cup championship.
Gillis retired in 1987 then returned to the game a year later with Britain's Solhill Bulls. He also skated with the Peterborough Pirates then coached the Tellford Tigers in 1991-92 before leaving the ice to become a coach. He would later become very involved in the Scientology movement in Quebec.