Birger Nilsen competed in four events at the 1904 St. Louis Olympics. He competed in the individual all-around (82nd); the individual all-around, apparatus work (85th); the individual all-around, field sports (67th); and the team all-around, apparatus work and field sports (6th). Nilsen was born in Norway and was still a Norwegian citizen as late as when he registered for the US military draft for World War I. He represented the Brooklyn Norwegier Turnverein, however, at the 1904 Olympics. He worked in the US as a carpenter. In official sources, his name is listed in various ways – Birger, Berger, Bergin, and Nilsen, Nielsen, Nelsen.