Armstrong was born in
Bennington, Vermont on April 19, 1903, the son of Marcus P. Armstrong (1864–1928) and Alice J. Cordes (1868–1953). He graduated from Bennington High School in 1922, and attended the
University of Vermont from 1922 to 1923. He decided on a legal career, and
studied law with Harry Chase of Bennington, and in the
Ludlow office of
William W. Stickney and
John G. Sargent. Armstrong was
admitted to the bar in 1926. A Republican, Armstrong served as second assistant clerk of the
Vermont House of Representatives in 1925, and was the House Clerk from 1927 to 1935. He was Secretary of Civil and Military Affairs (chief assistant) to Governor
Charles Manley Smith from 1935 to 1936. Armstrong was Vermont's deputy Commissioner of Industries in 1936. He served as commissioner from 1936 to 1939, and Commissioner of Industrial Relations from 1939 to 1949. In 1948, Armstrong was the successful Republican nominee for Secretary of State. He was reelected seven times, and served from January 1949 to January 1965. Armstrong was defeated by Harry H. Cooley during the
Democratic landslide of 1964, which was the first time a
Democrat had ever won the Secretary of State's office. In 1968, Republican
Richard C. Thomas won the Secretary of State's position. He employed former Secretaries Armstrong and
Helen E. Burbank on a consulting basis at the start of his eight-year tenure. ==Retirement==