Gustafson has been working as an actor since 1953. In 1957, he was hired for the Swedish royal theater Dramaten and also began performing in television plays. His TV debut was in 1955 in a small part in Hamlet. In Sweden, he is best known for the role of Dynamit-Harry from the Jönssonligan movies, a Swedish remake of the Danish Olsen Banden movies. Another role that he is known for in the Nordic countries is the role of Alfred in the TV series and movies about Emil i Lönneberga, based on stories written by Astrid Lindgren.
Gustfason's long film career also included a supporting role in the 1992 Ingmar Bergman scripted Den goda viljan (The Best of Intentions), having previously been directed by Bergman in a 1983 TV version of Moliere's The School for Wives. His voice work includes Alfons Åberg short movies, Pelle Svanslös (Peter No-Tail), and Disney's Robin Hood as Friar Tuck.