He continued in a variety of B pictures such as Prison Farm and King of Alcatraz before appearing in two of Cecil B. DeMille's films The Buccaneer (1938) and North West Mounted Police (1940).

[1] Following his military service, Hart worked frequently for Sam Katzman; he was given the lead role in the Jack Armstrong (1947) film serial.

Based on the assumption that the masked character, rather than the actor, was the true star of The Lone Ranger, the program's producers fired Moore (presumably over salary differences) and replaced him with Hart, who was of a similar build and had a comparable background in Westerns.

In 1955, Hart starred in the serial The Adventures of Captain Africa, which was originally intended to be a new movie about famous comic book hero The Phantom.

Interviewed by Tom Weaver in "Western Clippings" magazine (May–June 2000), Hart revealed that he met actress Beryl Braithwaite when she played a role in an episode of the series; they married just days later, with "Hawkeye" co-star Lon Chaney Jr., the best man at the wedding.

In 1965 Hart made two brief appearances on the TV series Perry Mason, including the role of title character and murder victim Jamison Selff in "The Case of the Wrathful Wraith."

On September 20, 2009, Hart died from complications of dementia at his home in Playas de Rosarito, Baja California, Mexico at the age of 91.