Parallel to his studies, Sønstevold played piano and trombone in one of the leading jazz quartet of the era: Funny Boys (1932–39).

After the outbreak of World War II, Sønstevold fled to Sweden where he subsequently met the composer Maj Lundén whom he married in 1941.

[3] From 1946 to 1969, Sønstevold composed music for 40 motion pictures and three full-length documentaries.

As a theatre composer, Sønstevold penned the score for Jens Bjørneboe’s Semmelweis, Henrik Ibsen’s Catalina, Tarjei Vesaas’ Bleikeplassen as well as Georg Büchner’s Woyzek.

When Sønstevold composed the music for Det Norske Teatret’s 1957 performance of William Shakespeare’s The Tempest, he was one of the first Norwegian composers to utilize electronic elements in his music.