Draughtsman for wood engravings and watercolourist. Elder brother of John Everett Millais. Worked at Farnham, specialising in landscape paintings.

The little that is known of Millais's elder brother is gleaned from incidental references in J. G. Millais's life of his father. In the early 1850s the two brothers were much together: William was one of the party at Ewell in the summer of 1851, along with his brother, Holman Hunt and Charles Collins, and two years later accompanied his brother to Scotland.