Born in South Africa, Lewis was educated there and later at the Slade School in London.  He studied with Stanhope FORBES at Newlyn c1910-14, and married a fellow student from Ireland. In WWI he served in the armed forces in France, Belgium and Italy, and during WWII was an official war artist for the South African forces.

His first marriage broke up in 1922, and he was left with three small children. He sent his two sons, Tom and David, home to Cape Town for relatives to raise, although he visited regularly. His daughter, Catherine, remained in London with his ex-wife. He married Vera Player in 1933, and they settled in Chelsea with the return of one of his sons from South Africa. He frequently painted black South African subjects.