He is the younger brother of the acclaimed Bergen Guitarist Ole Thomsen. When growing up, he was inspired by Jazz fusion and played in bands like "Rabies" (including drummer Atle Garmann & bassist Knut Vaksdal), and "One Step Limbo" together with Program 81/82 vocalist Kate Augestad and bassist Frank Hovland among others,
In 1987 Thomsen appeared on the show "Nattsang" at Norsk Rikskringkasting, within the band "Growl", comprising Karl Seglem (saxophone), Vigleik Storaas (piano), Odd Magne Gridseth (bass) and Terje Isungset (drums) in addition. In addition Thomsen has several performances at the Bergen Jazz Festival Nattjazz.
Within the band "Tundra" (1984), "Growl" (1986-1987), "Poems for Trio" (1986-1993, 1989-1991 with Frode Rasmussen), "Hip Slippers" (1991), and "Frank"s Friends North"Loose Ends" (1993).