Adopting the stage name Willard Mack, after graduation he took minor acting jobs for a few years and did Shakespearian repertoire.

However, writing scripts was what he was most interested in, and his second effort, about the North-West Mounted Police, In Wyoming, was a commercial success and was later the basis for his film Nanette of the Wilds.

Mack coached Stevens's acting and rewrote parts of the play to expand her role and then persuaded her to change her name to Barbara Stanwyck.

During his time on Broadway, Mack began writing for motion pictures, and although he performed in fifteen films and directed four, he was primarily a writer.

He then wrote and directed Broadway to Hollywood, a backstage musical that spanned nearly five decades recounting the struggles of a vaudeville family.