Forsling, a defenseman, was born in Linkoping, Sweden, and came up through the local hockey club. He made his Swedish Hockey League debut with Linkoping during the 2014-15 season, a few months after the Vancouver Canucks selected him in the fifth round (No. 124) of the 2014 NHL Draft.
The Chicago Blackhawks acquired Forsling on Jan. 29, 2015, in a trade for forward Adam Clendening; he signed with Chicago on May 11, 2016, was on the opening night roster for the 2016-17 season and scored his first NHL goal on Jan. 6, 2017. He ended up splitting the season between Chicago and Rockford of the American Hockey League.