It is said he first appeared upon the stage in the arms of his mother, Mary Stafford Cooper, at the age of eighteen months when the comic opera Castle Grim was performed in Dublin.

[1][2] Cooper was active in American stock and repertoire theater with Russ Whytal, Frederick Freeman Proctor, and Charles Dillingham's companies.

[4][5] Cooper's motion picture career began around 1908 when he helped make Chronophone synchronized sound films for Gaumont which had established a studio in Flushing, New York, recording short songs and vaudeville routines.

This early form of sound film was not successful in the United States, in part due to Thomas Edison's obstruction, and Gaumont abandoned American production in 1910.

[10] In 1930 he became a radio actor, playing Pegleg Gladdis the patriarch of a hillbilly family in the half-hour serial drama Moonshine and Honeysuckle broadcast on the NBC Red network on Sunday afternoons.