Thwaites wrote popular adventure novels, selling over four million copies. He was best known for his first work The Broken Melody, written when he was 19. It was originally self-published but became a best seller, selling 55,000 copies in Australia and adapted into a 1938 film.

In February 1933 Thwaites moved to England to for Elstree Studios. He spent several months there and several months in Hollywood, attempting unsuccessfully to sell his work to movie producers.

He returned to Australia in late 1933 and sought out manuscripts to publish. In 1936 he founded his own publishing firm. F. J. Thwaites.

In May 1937 he joined Adelaide radio station 5KA as production manager.

In 1938, Thwaites left for England via the Pacific Islands and Panama Canal, researching material for novels.

During the forties and fifties, many of his works were adapted for radio.

In late 1954 Thwaites set up a company in England, Harcourt Press, to publish his books there.

In the late 1960s Thwaites was financing and managing housing projects.