He served as the head football coach at the University of Utah from 1925 to 1949, compiling a record of 141–55–15.

Armstrong's 25-year tenure is the longest of any Utah Utes football head coach and his 141 wins are the second most in program history.

Armstrong also coached Utah's basketball and track teams and served as the school's athletic director.

He attended Drake University, where he played college football as a fullback.

Armstrong died of pneumonia, on September 4, 1983, at the Flagship Convalescent Home in Corona Del Mar, California.