He was best known for his collaborations with Jack Webb, and he frequently portrayed law enforcement officers in film and television.

Ellis and Webb together devised the name and concept for Dragnet[3] after collaborating on an unsuccessful project titled Joe Friday, Room Five.

[4] He played Officer Frank Smith in eight episodes of the original Dragnet series.

's Man, and he played Beat bistro owner, painter and sculptor Wilbur in five episodes of Peter Gunn.

From 1959 to 1962, Ellis was cast as Dr. Dan Wagner in seven episodes of the CBS military sitcom/drama series, Hennesey, starring Jackie Cooper as a United States Navy physician, with Abby Dalton as nurse Martha Hale.