He moved to California and trained drama at the prestigious acting school Pasadena Playhouse College of Theatre Arts, where he changed his first name to Todd.

[2] Armstrong’s wealthy parents set him up with a trust fund but after a couple of years with no success landing acting roles, he took part-time work as a landscape gardener.

Henry learned of her gardener's acting aspirations and was impressed enough by Armstrong's good looks to arrange for him to get a screen test at Columbia Pictures, where she was under contract.

In 1962, Armstrong made his film debut with a small role in director Edward Dmytryk's drama Walk on the Wild Side (sole credit as Todd Anderson).

Todd had only one additional leading role, in the 1965 World War II film King Rat, after which he receded to supporting parts in pictures such as Dead Heat on a Merry-Go-Round (1966), and gradually moved back into television work.