Forsling found his NHL home in South Florida when he signed an eight-year contract March 7, 2024, cementing himself as a reliable defenseman since the Panthers claimed him off waivers from the Carolina Hurricanes on Jan. 9, 2021. At the time of the signing, Forsling led Florida at his position in points, shots on goal, and the NHL at plus-44, earning praise from general manager Bill Zito as one whose "career is an example of how far hard work and total commitment to improvement can take a person."

Forsling led Panthers defensemen in scoring (13 points) in the 2024 Stanley Cup Playoffs en route to becoming a Stanley Cup champion while setting a team record at his position for assists (nine) in one playoff year. His goal at 18:27 of the third period to defeat the Boston Bruins 2-1 in Game 6 of the Eastern Conference Second Round made him the second player in Panthers history to score a series-clinching goal in the final two minutes of regulation.

During the 2024-25 season, Forsling was named to Sweden's roster for the 4 Nations Face-Off. He also led the Panthers with 35 blocked shots and was third on Florida in ice time per game in the playoffs (23:17) to help Florida win the Stanley Cup again.

He 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.

Forsling played most of 2017-18 with the Blackhawks, finishing with 13 points (three goals, 10 assists) in 41 games.