Stark has collaborated with the illustrators Anna Höglund and Mati Lepp.
From 1989 to 1998 he was an elected member of the Swedish Academy for Children's Books Svenska barnboksakademin.
In 1998 he received the Nordic Children's Book Prize.
Stark was born and grew up in Stureby, Stockholm Municipality, which place features in several of his books. Stark's interest in writing started early; during his time at secondary school he was introduced to writing by his classmate Peter Curman, and in 1964 he wrote his first poetry Ett hål till livet. Following this, Stark's interest in writing for a career was greatly encouraged.