Entering films as one of Mack Sennett's Keystone Cops in 1913, Cline began assisting Sennett and by 1916 was directing shorts at Keystone. In the early '20s he co-wrote and co-directed seventeen of Buster Keaton's shorts, including such classics as The Playhouse, The Boat, and Cops, as well as Keaton's first feature, the Intolerance-parody The Three Ages. Later in the decade he was reunited with Sennett when he directed two-reelers for such comics as Ben Turpin and Carole Lombard. In 1932 Cline directed W.C. Fields in the memorable satire Million Dollar Legs and became one of the few directors whom the irascible comedian could tolerate. Called in to helm most of Fields' scenes in You Can't Cheat an Honest Man (signed by George Marshall), Cline went on to direct the classic features that capped Fields' career in the early '40s: My Little Chickadee (co-starring Mae West), The Bank Dick, and Never Give a Sucker an Even Break. Cline's last important work was with Olsen and Johnson on Crazy House and Ghost Catchers. He ended his career with Monogram's low-budget "Jiggs & Maggie" comedy programmers.