[1] His family moved to Sandane in Gloppen where he spent his youth, but he was later a freelance musician resident of Oslo since 2003.

Since 2006 he has been engaged as Lecturer in saxophone and jazz improvisation at Norges Musikkhøgskole, since 2010 also at Department of Musicology Universitetet i Oslo.

He also works as an arranger, much in connection with horn section or big band.

Halvorsen plays with "Ensemble Denada", "Examination of What", Ole Børud, "Ekvilibrium", "Vinni", "Penthouse Playboys", "Hans Orkester", "Steffen Isaksens Orkester", "KABA Orchestra" and "Jon Haaland Big Band".

Has also appeared in the bands Paperboys, Dance with a Stranger, Karpe Diem, Sharp Nine, "Smiths Venner", Jens Wendelboe Crazy Energy Orchestra, "Mathilde Grooss Viddal/FriEnsemblet", Kjell Karlsens Orkester, "Bjørn W W Jørgensen Storband", Chipahua, The New Swing Generation, "The Fabulous Couldhavebeens", "The New Jordal Swingers", "Soulslave", The Sinatra Songbook, "Soul, Inc.", "Soul Insurance" and "Earplay", and is also musical director of the Big Band "Bjørvika Business Band" since 2010.