He previously played for the Chicago Blackhawks, Calgary Flames, Philadelphia Flyers, Montreal Canadiens, Washington Capitals, Toronto Maple Leafs, and New York Rangers.

[2] Gustafsson was called to make his Elitserien (now the Swedish Hockey League (SHL)) debut in the 2011–12 season opener against HV71 on 15 September 2011, but did not receive any game-time.

[5] After two successful seasons establishing himself with Frölunda, and with his NHL playing rights not retained by Edmonton, on 30 April 2015, Gustafsson signed a two-year contract with the Chicago Blackhawks.

[6] Gustafsson began the 2017–18 season with Chicago's American Hockey League (AHL) affiliate, the Rockford IceHogs, but was recalled to the NHL on 9 January 2018.

Adding 6 goals and 26 points in 59 games and with the Blackhawks out of contention for a playoff berth, Gustafsson was dealt by Chicago at the NHL trade deadline to the Calgary Flames in exchange for a 2020 third-round pick on 24 February 2020.

[17] With his ice-time elevated due to an injury to leading defenceman John Carlson, Gustafsson was rejuvenated with the Capitals, scoring 7 goals and 31 assist for 38 points in 61 regular season games.