He played every season in the league from 1990 to 2006, as a member of the Winnipeg Blue Bombers, BC Lions, Edmonton Eskimos, Hamilton Tiger-Cats, and finally with the Calgary Stampeders.

He is a five-time Grey Cup champion, having won three times as a player and twice in a front office capacity.

In 1987, he started every game for Florida State, leading them to an 11–1 record and a spot in the Fiesta Bowl, which they won 31–28 over the University of Nebraska.

[2] He made the Chiefs out of training camp, and spent his first, and only, National Football League season on the bench as the third quarterback.

Unable to find a place to play in 1989, McManus signed with the Canadian Football League's Winnipeg Blue Bombers in time for the 1990 season.

In the 82nd Grey Cup, Austin was knocked out of the game and McManus had to take over at halftime, and ended up leading the Lions on a drive downfield setting up Lui Passaglia to kick a game-winning field goal, giving BC a 26–23 victory over the Baltimore Stallions.

Any animosity McManus must have felt to the Eskimos must have quickly cooled, however, as he signed with Edmonton during the off-season as a free agent following his release by British Columbia.

In the West Semi-Final at Commonwealth Stadium in Edmonton, the Eskimos slaughtered McManus’ former team, the Winnipeg Blue Bombers, 68–7.

McManus left the Eskimos as a free agent for 1998, as the Hamilton Tiger-Cats signed both the veteran quarterback and his all-time favorite receiver, Darren Flutie.

The Tiger-Cats warred with the fast-rising Montreal Alouettes and their veteran quarterback Anthony Calvillo all season, including a rare tie in a regular-season meeting between the two teams.

The icing on the cake came on the 87th Grey Cup, where McManus thwarted the Stampeders' drive for a repeat in a rematch of the previous year's championship game.

Garcia was gone to the NFL but his replacement Dave Dickenson had proven very dangerous; however, the Tiger-Cats took their first Grey Cup since 1986 with a 32–21 victory.

But, after their Grey Cup victory, the Tiger-Cats were beginning to enter a long spiral to the East Division basement.

Despite starting fifteen games, McManus threw for only 2,869 yards, snapping his record streak of consecutive 4,000-yard seasons at eight.

The Tiger-Cats shocked the Canadian football world by finishing 9–8–1, an accomplishment amazing enough for rookie head coach Greg Marshall to be named coach of the year and McManus to receive the Rogers-AT&T Fan Choice Award, sharing it with Anthony Calvillo.

The Tiger-Cats were unable to build on their 2004 success, and in the 2005 season finished in the league's basement at 5–13, with a defense that allowed 583 points.

McManus threw for 2,544 yards and eleven touchdowns with a quarterback rating of 67.1, and spent time on the bench in favor of Khari Jones, Marcus Brady, and the unknown Kevin Eakin who all took snaps.

[6] On December 2, 2013, it was announced that McManus has been hired as the assistant general manager and director of U.S. scouting for the Winnipeg Blue Bombers.