Born in China in 1914, Mellis studied at Edinburgh College of Art from 1930-34 under Peploe, Gillies and Maxwell, and was a contemporary of Gear and Barns-Graham. She met Adrian Stokes in 1938 and after they married and moved to London, she studied at the Euston Road School. Shortly after, they moved to St Ives where Mellis became instrumental in setting up the St. Ives School of artists, with friends Ben Nicholson and Barbara Hepworth. She later left Cornwall in 1946, and married painter Francis Davidson. They moved to Southwold, where she started to create her driftwood sculptures. She died in 2009.