John was born in Tenby in Wales. He was brother of the artist Gwen John (1876-1939) and attended the Slade School of Fine Art where he won a Scholarship in 1896. From early in his career he was recognised amongst his peers as a talented draughtsman. His best known works are of his second wife, Dorelia, his children and his sister Gwen. John was widely exhibited during his lifetime and was a notorious figure in the London art world. He has work in many galleries including Tate Britain and the National Gallery.