Gwendolen Mary John (22 June 1876 – 18 September 1939) was a Welsh artist who worked in France for most of her career. Her paintings, mainly portraits of anonymous female sitters, are rendered in a range of closely related tones. Although she was overshadowed during her lifetime by her brother Augustus John, her reputation has grown steadily since her death.

John's pictures are held in many public collections. Some of the best examples are in the National Museum Cardiff and in Tate Britain, London.