As a youth, Harry Siljander was a promising speed skater and swimmer and took up boxing in 1940, while serving in the Finnish Army. In 1943, Siljander won the Finnish Army Championships as a middleweight and in 1946 he won his first medal, a silver in middleweight, at the Finnish Championships. In 1947, Siljander switched to light-heavyweight and won five Finnish titles in that category from 1947-50 and 1952. Siljander was also selected to the Finnish 1952 Olympic team and won a bronze medal, losing his semi-final match to the eventual gold medal winner, American Norvel Lee. After the Olympics, Siljander retired from boxing and later worked as a butcher in the Hietalahti market in Helsinki until his retirement in 1986. Siljander was selected to the Finnish Boxing Hall of Fame in 2005.