When it came time to enter the junior ranks, the two parted company for a few years while Roberts joined the Ottawa 67's of the OHL. In his second year with the club, in 1983-84, the 67's won the Memorial Cup. Several seasons later, after a standout career in Ottawa, Roberts joined the Guelph Platers late in the season. He arrived just in time to savour his second Memorial Cup win.

Ready to turn pro, Roberts split his first season between the Calgary Flames, who had drafted him, and the Moncton Golden Flames of the AHL. His stay in the minors was short, however, as he caught on permanently with the Flames in 1987-88, about the same time his childhood buddy, Nieuwendyk, arrived as well.

From that point forward, Roberts established himself as a rambunctious player, known for his hard drives towards the opponent's net. In fact, his first-ever NHL goal was scored against the Vancouver Canucks. He put himself and the puck behind the goal line.

Roberts' second full year with the Flames brought him to the top as the club secured its first and only Stanley Cup victory. After the big win, he only got better as the years progressed. In 1991-92, he reached his height of personal output, scoring 53 goals in one campaign.

Several seasons later, however, all of the hard drives and hits taken from behind caught up with him. He missed most of the 1994-95 season with the hope that a long rest would ease the burning pain in his neck and numbness in his arm. He attempted a comeback the following year, but found that his symptoms got worse. A closer check by doctors revealed bone spurs and nerve damage in his neck. The operation required to correct the situation would be delicate and could offer no guarantee that Roberts would ever play pro hockey again.

He sat out the 1996-97 campaign and embarked on a vigourous reconditioning program. With his new super healthy regime in place, Roberts made a comeback as a free agent with the Carolina Hurricanes. With his neck built up like that of a bulldog's, Roberts was back in the league's goal creases engaged in territorial jousting. Over the three-plus seasons since his operation, he has played solid hockey, netting his usual 55 to 60 points per campaign.

In 2000, Roberts accepted a lucrative offer to sign as a free agent with the Toronto Maple Leafs and during the 2002 Stanley Cup playoffs was the team's leading point getter and its best player. In the summer of 2002 Roberts underwent shoulder surgery and missed the better part of the 2002-03 season, before returning in the latter stages of the season and post season.

In 2003-04, Roberts surpassed the 1,000 games played plateau and notched his 800th point. Following a washed out NHL season in 2004-05, Roberts was acquired by the Florida Panthers in the summer of 2005.

As a member of the Florida Panthers, Roberts would help lead a group of young players as he entered into his 18th NHL season. The club would fail to make the playoffs in the 2005-06 season and mid-way through the following season Roberts was rumoured to be traded. As the NHL trade deadline approached, many reports suggested Roberts would have liked to be dealt to Toronto or Ottawa. The Panthers explored both options, but sent him to the Pittsburgh Penguins in exchange for Noah Welch. In Pittsburgh Gary Roberts is expected to help lead a group of young superstars including Sidney Crosby, Evgeni Malkin, and Jordan Staal.

Over two injury plagued seasons in Pittsburgh, Roberts managed to notch his 900th career NHL point and would be considered one of the best leaders & mentors the Penguins' ever had. After a magical run to the Cup Finals in 2008, Roberts was acquired by the Tampa Bay Lightning where he would play the final 30 games of his career before retiring in March of 2009.