Born in Kyrksæterøra, Forren was originally a youth player at local club KIL/Hemne, before starting his professional career with Molde in 2007.

After making over 150 appearances for Molde, he joined Southampton in January 2013 for a fee in the region of £4 million, but ended up not playing a single game.

Alongside Trond Strande and Mattias Moström, he is the only player to have appearances for Molde in 12 consecutive Eliteserien seasons.

He took the Tippeligaen by storm and European clubs as A.C. Milan, Newcastle,[4] Liverpool[5] and Hoffenheim,[6] have watched him playing for Molde.

But Forren stated that he wanted to stay in Molde for a while, even though his dream was to eventually play in a bigger European league.

[10] On 18 January 2013, Forren signed for Premier League side Southampton on a three-and-a-half-year deal for an undisclosed fee.

[13] Rumoured to make a return move back to Molde, Forren insisted he wanted to stay at Southampton to fight for his place.

[27][28] On 11 January 2023, Klaksvíkar Ítróttarfelag of the Faroe Islands Premier League announced the signing of Forren to a one-year contract.