Born in Pennsylvania, Williamson moved with his family to Milwaukee, Wisconsin. His father died when he was eleven years old. He acted in amateur theatricals and joined a local theatre company as a call-boy at the age of 15, soon taking roles and eventually moving to New York where he played for several years at Wallack's Theatre and then other New York theatres. In 1871, he became the leading comedian at the California Theatre in San Francisco and the next year married comedian and actress Maggie Moore.