Bellamy was born in Hillsboro, Texas as Margaret Derden Philpott.
She ran away to New York City at age 17, and soon was working as an actor and dancer on Broadway. After various stage work she made her film debut in 1920. She became a Hollywood star of the silent movie era. After 4 years with Famous Players her contract was picked up by Fox Films.
She at first made the transition to sound film starting in 1928, but the next year after an arguement with the Fox Studio demanded her contract be torn up and left the studio. The move left her out of work until she agreed to return to Hollywood in 1932, demoted to appearing in low-budget "B" pictures.