William George Gillies was born in Haddington, East Lothian. As a boy he was introduced to outdoor painting by accompanying both his uncle, William Ryle Smith, and the amateur painter, Robert Alexander Dakers, on painting expeditions in the surrounding countryside. In 1916 he enrolled at Edinburgh College of Art but didn’t graduate until 1922 due to two years spent serving during the First World War. Following graduation he founded the 1922 Group with nine other artists, including William Crozier and William MacTaggart and he went on to exhibit with them annually from 1923 to 1929. In 1923 he travelled to Paris on a postgraduate scholarship where he studied under André Lhote. Before returning to Scotland the following year, he also travelled to Italy where he visited Florence, Venice, Padua and Ravenna. After his travels he briefly painted in a cubist manner but later criticised the training he had received in Paris and reverted back to a more traditional style.  He returned to Edinburgh in 1925 to take up a teaching post at Edinburgh College of Art where he worked for over forty years.

Sharing a studio with MacTaggart from 1931, the same year in which he saw an exhibition of the work of the Expressionist Edvard Munch, he started to develop a loose expressionist painting style which he executed on his regular trips around Scotland to paint the landscape. He continued to develop this style throughout the 1930s, eventually moving to a village in MidLothian in 1939 where the border landscape became the subject of his later work. Seven years later, he was made head of the School of Drawing and Painting at Edinburgh College of Art, becoming its principal in 1959 and remaining there until retirement in 1967.

Gillies was appointed CBE IN 1957 and was knighted in 1971 followed by an appointment to Royal Academician the following year. He also received an honorary DLitt from the University of Edinburgh in 1966 and he was elected a fellow of the Educational Institute of Scotland in the same year.

Gillies painted right up to his death in 1973 and, despite his teaching commitments, his output was prolific. Although he painted some portraits most of his work is landscapes and still lifes painted in oils or watercolour. He exhibited with the Society of Eight, the Society of Scottish Artists, the Royal Scottish Academy, the Royal Scottish Society of Painters in Watercolour as well as several solo exhibitions at the Scottish Gallery, Edinburgh. Much of his work is represented in the Royal Scottish Academy and the Scottish National Gallery of Modern Art.