Ensio Siilasvuo enlisted in the Finnish Army in 1940 and served as a chief-of-staff of an infantry regiment in 1945. He was promoted to captain at the age of 22 and was wounded twice.
After the war he led several UN missions. He was the Commander of the Finnish Contingent to Cyprus in 1965, UNFICYP. He served in a variety of positions in the Middle-East after the Six-day War. He was Commander of the UNEF II in Sinai Peninsula from the end of the October War (1973) till August 1975. In August 1975 he was assigned to the new post of Chief Coordinator of the United Nations Peacekeeping Missions in the Middle East, which he held until peace was reached between Egypt and Israel in 1979. He retired in 1980.
He was promoted to the rank of full general on October 6, 1998.