FK Bodø/Glimt
Forn hails from Kvæfjord and played for Harstad IL before joining FK Bodø/Glimt ahead of the 2008 season. He did not establish himself in the first team, and was in 2009 loaned out to Alta IF. In 2012, he joined Mjøndalen IF, and eventually played as a first-choice goalkeeper in their 2015 Tippeligaen stint. On 3 May 2016 he retired from football on top level.