Mack began his theatrical career in traveling productions, working with the companies of actors such as Clay Clement and Walker Whiteside and appearing in such plays as The Orphan of Geneva, The New Dominion, and A Southern Gentleman.

[3][4] In 1902 he joined the company of Minnie Maddern Fiske and began appearing in her Broadway productions.

He abruptly left Fiske's company in December 1906 to take a role in Clyde Fitch's The Truth.

[3][5] Mack began taking roles in silent films in 1919, when he appeared in Virtuous Men.

[4] He attended the University of Michigan,[4] and was a longtime member of The Lambs, a theatrical society.