[1] Gustavsson played for the Toronto Maple Leafs, Detroit Red Wings, Boston Bruins and Edmonton Oilers during his National Hockey League (NHL) career.

After overcoming a groin strain, on 1 December, Gustavsson left after the first period in a game against the Montreal Canadiens with a heart murmur, which led to a second Radio Frequency ablation to treat a reentrant tachycardia.

He won seven straight starts in March to tie the Maple Leafs’ club record for the longest winning streak by a rookie goaltender.

"[5] After becoming a restricted free agent in the summer, Gustavsson agreed a two-year extension with the Leafs on 15 April 2010, with an average salary of $1.35 million per year.

[6] In the following 2010–11 season, on 4 February 2011, he was sent down to the Toronto Marlies, the American Hockey League (AHL) affiliate farm team of the Maple Leafs, for a two-week conditioning stint.

Two days later, on 11 February, Gustavsson underwent a third minor heart ablation surgery and was placed on injured reserve by the Maple Leafs, suspending his conditioning stint.

On 23 June 2012, with Gustavsson soon to be eligible for free agency, the goaltender's rights were traded by the Maple Leafs to the Winnipeg Jets for a conditional seventh round pick in the 2013 NHL Entry Draft.

Gustavsson posted a 3–0–0 record with a 1.67 goals-against average and .953 save percentage in victories over the Boston Bruins, Columbus Blue Jackets and the Colorado Avalanche, helping the Red Wings move into first place in the Atlantic Division.

[17] On 1 July 2016, having concluded his contract with the Bruins, Gustavsson signed as a free agent to a one-year deal with the Edmonton Oilers to provide backup to starting goaltender Cam Talbot.

[19] After closing out the 2016–17 season, with the Condors in the AHL and having not been recalled to the Oilers post-season roster, Gustavsson as a pending free agent agreed to return to the SHL, in signing a three-year deal to be the starting goaltender for Linköping HC on 4 May 2017.

He resides outside of Detroit, Michigan, with his wife, Emelie Witt, to whom he was married on 19 March 2013, by United States District Judge Stephen J. Murphy.