Sonstad is one of Norway’s most sought after cello players. He has been a soloist with several of the leading orchestras in Norway. Since co-founding the Oslo String Quartet in 1991 he has built up a considerable reputation as a chamber musician. Sonstad is very active as an arranger and composer. He has written incidental music for three theatre productions in Copenhagen and his brilliant arrangements for the Oslo String Quartet and others in all genres and styles have made headlines through recordings and concerts.