The 27-year-old left-shot defenceman is a pending unrestricted free agent and considering the Blackhawks have fallen back in the Western Conference wild-card race, he was expected to be moved.
Gustafsson had been with Chicago since 2015. The Nynashamn, Sweden native had a career-high 17 goals and 43 assists in 79 games in 2018-19 and was leading all Blackhawks blueliners with 26 points through 59 games with Chicago this season.
With Mark Giordano and Travis Hamonic on injured reserve, Flames general manager Brad Treliving hoped to fortify his team’s back end.
The team also agreed to a deal to acquire Derek Forbort from the Los Angeles Kings on Monday.