Born in Oslo, where he studied under the watchful eye of Finn Mortensen and Olav Anton Thommessen. At the University of California, his mentors included Roger Reynolds and Vinko Globokar.
Wallin's music combines intuitive freedom with a rigorous mathematical approach. He uses fractal algorithms to create melodies and harmonies, and his compositions refer to the achievements of Ligeti, Xenakis and Berio.
His work won him the Norwegian Composers' Association Award (1987) and the Nordic Council Music Award (1998).