Trimble began his film career directing Jean, the Vitagraph Dog, the first canine to have a leading role in motion pictures.

As he chatted with the sole assistant working under Rollin S. Sturgeon, head of the scenario department, he learned that a story of special interest to producer Albert E. Smith had been set aside because it required a dog that could act—not simply do tricks, but to behave naturally on command.

[5]: 44 Trimble asked if there were any dogs around, and was told about a stray that hid in the garage and came out only to snatch scraps left by members of the crew.

[6] He became one of the studio's leading directors, responsible for all of Jean's films and most of those made by Florence Turner, John Bunny[4]: 139  and Flora Finch.

[4]: 36  Trimble later explained that they went to England because in 1913 "the power of large companies [in the U.S.] left slight opportunity for an independent producer with small capital.

"[4]: 37  Already famous from her Vitagraph films, Turner introduced herself to British audiences with a personal appearance at the London Pavilion on May 26, 1913.

[4]: 37 In August 1916, Trimble left his wife in England and returned to the U.S.[4]: 38  with his daughter[9] and his canine star Jean, who died later that year.

[6] He directed Fool's Gold (1919), an independent production partially filmed in the Cascade Mountains in Washington state, in which Turner tried to return to starring roles in American motion pictures.

[22][23] Trimble trained the dog and directed him in four rugged outdoor adventure pictures that were shot on location: The Silent Call (1921), Brawn of the North (1922), The Love Master (1924) and White Fang (1925).

The Hazel Hurst Foundation educated and found employment for the blind, including injured war veterans, and trained German Shepherds as assistance dogs that were given free to each student.

By August 1944 the school had supplied the Lockheed-Vega Aircraft Corporation with 300 workers, greatly needed for production work during World War II.

"[30] Trimble died from a heart ailment on February 8, 1954, at age 68, at the Motion Picture Country House and Hospital in Woodland Hills, California.