Born in Haddington near Edinburgh, Gillies studied at Edinburgh College of Art. After graduating, he taught there for more than forty years until his retirement as Principal in 1966, having influenced several generations of artists. A college grant enabled Gillies to go to Paris in 1923 to study, and for a brief period he worked in a cubist style. But, by nature, he was more inclined to the traditional, and in his later work only his still lifes show a general debt to Cubism. Gillies concentrated on landscapes and still lifes, and was particularly fond of depicting the Lothian, Fife and Border regions.