Alfred Engelsen competed in two sports at the 1912 Stockholm Olympics: in gymnastics, he won gold as a member of the Norwegian team in the free system all-around; in the plain high diving, he was eliminated in round one. In diving, he won a total of eight Norwegian championships: in plain high diving in 1916 and 1919, in platform diving in 1913, 1918, 1919, 1922 and 1923, and in the combined event in 1922.
The son of a sailmaker in Bergen, Engelsen learned the trade and became a master like his father. In 1926, he married Orlaug Hofstad in his hometown and had no children. Engelsen spent his later life in Tvedestrand on the Norwegian southeast coast.