He worked for a time in a film laboratory and while there was offered a screen test, after being discovered at Harold Lloyd's Beverly Hills Little Theatre for Professionals.

He spent much of his career in westerns, including a stint in the mid-1930s as Johnny Nelson, the sidekick of Hopalong Cassidy in Paramount's highly successful series.

Ellison spent most of the remainder of his career shuttling between cowboy pictures and more varied roles, primarily in B movies like The Carter Case and The Undying Monster.

He had a supporting role in 1941's Charley's Aunt (which starred Jack Benny) and played the romantic lead in 1943's The Gang's All Here, a Twentieth Century Fox musical in which he seemed somewhat lost among the vivid antics of Carmen Miranda, Charlotte Greenwood, and Edward Everett Horton (and was the only principal not to sing a note).

Ellison landed another romantic lead role as Jerry Gibson in the musical film Lady, Let's Dance (1944) which starred ice-skating sensation Belita.