Dwan's career spanned the history of American motion pictures, from the days of silent one-reelers to modern Technicolor features that utilized some of the cinematic techniques whose use he had pioneered. By his own estimate, Dwan participated in the making of 1,850 films, some 400 of these as a director. (Only a few of his works remain extant.)
In 1911 he moved to the American Film Company, where he got the opportunity to direct when the person originally given the assignment was discovered drunk. Dwan made more than 250 films there, mostly one- reel westerns, which he later recalled "the actors showed me how to direct."
It was Dwan's engineering skills that were particularly useful to him: he is credited with mounting a camera on a car and inventing the dolly shot. He proposed the construction of a rail system on the set of Griffith's "Intolerance" and years later developed techniques for on-set sound recording.
In 1913 Dwan joined Universal, where he worked with Lon Chaney and met his first wife, Pauline Bush. Later that decade he began making films with Douglas Fairbanks and Gloria Swanson.
Although he made a successful transition to sound, Dwan was relegated for a number of years to the directing of programmers at Fox. Despite his commercial success with several Shirley Temple films, most of his work was confined to the grind of B pictures. He may have been comfortable with this, as he later remarked: "If you get your head up above the mob, they try to knock it off. If you stay down, you last forever."
Dwan later went to work at Republic, where his "The Sands of Iwo Jima" (1949) helped make John Wayne the mythic American war-hero. Dwan described the old Hollywood this way: "Years ago we had no supervision. We made pictures our own way. We pleased nobody but ourselves and the public."