He played in the National Hockey League (NHL) for the Colorado Avalanche, St. Louis Blues, Buffalo Sabres, Minnesota Wild, Anaheim Ducks, Calgary Flames, and Philadelphia Flyers.

[4] Initially given the position with the Frontenacs as an energetic fighting role player, Stewart took advantage of his increased playing time and had a solid rookie season, scoring 18 goals and 30 points in 64 games.

Stewart played in his first NHL game that same night, getting no points and a –1 plus-minus rating in 7:29 ice time in the Avalanche's 2–1 shootout loss to the Dallas Stars.

He spent the majority of the season with the Avalanche, and on December 2, 2009, Stewart had another Gordie Howe hat trick while recording his first three-point game in a 6–5 shootout loss to the Florida Panthers.

Stewart finished the 2010–11 season with the St. Louis Blues and made an immediate impact in his debut with the team on February 19, 2011, scoring two goals against Timo Pielmeier in a 9–3 rout over the Anaheim Ducks.

Unable to adjust to the defensive tactics of renowned Head Coach Ken Hitchcock, he was increasingly subject to trade rumours whilst used in a diminished checking role and relegated as a healthy scratch during parts of the 2012 playoffs.

[13] With the commencement of the 2012–13 NHL lockout, Stewart signed a one-month contract, alongside childhood friend Wayne Simmonds, to play with the Eispiraten Crimmitschau of the 2nd Bundesliga in Germany on September 24, 2012.

[14] Becoming the most established NHL players in ETC Crimmitschau history, Stewart scored five goals and 11 points in nine games before he and Simmonds declined to extend their optional stint.

[15] Whilst opting to remain in Europe alongside Simmonds, Stewart signed to another lockout contract in the more competitive Czech Extraliga with HC Bílí Tygři Liberec on October 23, 2012.

[16] With the intention of playing alongside Simmonds and former NHLer Petr Nedvěd failing to materialize, and after five unfruitful games with Liberec, Stewart decided to return to Crimmitschau for the remainder of the lockout on November 13, 2012.

[17][18] Just under a month later, with new-found optimism of the lockout's end in sight and on advice to prevent injury, Stewart was released on his request from the remainder of his contract on December 7, 2012.

[22] A deadline rental for the Wild, Stewart was released to free agency and on July 12, 2015, signed a one-year, $1.7 million deal with the Anaheim Ducks.

As a free agent from the Flames, Stewart was un-signed over the summer, before opting to continue his professional career in Europe agreeing to a one-year deal with Slovakian club, HC Slovan Bratislava of the Kontinental Hockey League (KHL) on September 26, 2018.

[26] Stewart however never featured with Slovan, after he was initially reported missing by the club as a consequence of failing to attend the introductory press conference on October 3, 2018.

[28] On January 3, 2019, Stewart ended his brief retirement and signed for the Nottingham Panthers of the EIHL following in the footsteps of his elder brother who played there during the NHL lock-out in 2012.