From 1902 to 1904, he was the manager of the Cleveland Bronchos/Naps. Armour took over a Cleveland team with a losing record, and during his three years there, the team's record improved each year, reaching 86-65 in 1904. From 1905 to 1906, he was the manager of the Detroit Tigers. In his first year in Detroit, the team improved by 17 games over the prior year. With the signing of Ty Cobb, the Tigers set the table for three consecutive American League pennants that followed from 1907 to 1909. From 1907 to 1911, Armour served as the president and co-owner of the Toledo Mud Hens. He served as a scout for the St. Louis Cardinals in 1912 and next became business manager of the Milwaukee baseball club. He subsequently opened a restaurant in Minneapolis where he died in 1922 at age 53.