Born in Fife in 1915, Gear studied at Edinburgh College of Art from 1932. He expressed an early interest in Surrealism (which he soon abandoned) and had a brief brush with the Scottish Colourists when he was taught by SJ Peploe. Upon graduating, he won a travelling scholarship, taking him to Paris to study under Fernand Léger at the Académie Colarossi from 1932-37. Subsequently, he travelled and exhibited in Italy, Greece and the Balkans.

During 1945-1947, Gear travelled to Germany where he worked as a Monuments Man. From 1947-1950, he settled in Paris where he befriended Jean-Michel Atlan, Alan Davie, Hans Hartung and Pierre Soulages, among others. He became associated with the CoBrA group, a short-lived but important grouping of artists from Copenhagen, Brussels and Antwerp. Gear's Cobra paintings are considered a significant contribution to European 20th century painting. He also met Hans Hartung, Pierre Soulages and Serge Poliakoff and became part of the 'Art Informel' movement, a wide denomination for related types of Abstract Painting.

In 1958, Gear was appointed curator of Towner Art Gallery in Eastbourne. Gear resigned his post as curator in 1964 and became Head of the Faculty of Fine Art at Birmingham University, where he remained until 1975. From the 1970s until his death in 1997, Gear remained a firm Abstractionist and had a number of retrospective shows in various galleries and was part of many mixed CoBrA exhibitions.

The works of William Gear have been exhibited worldwide and are included in the following museum collections: City Museum and Art Gallery, Birmingham; Hunterian Art Gallery, Glasgow; Insituto de Arte Contemporaneo, Lima, Peru; Museum of Art, Ohio; Museum of Art, Tel Aviv; Museum of Modern Art, New York; National Gallery of Australia, Canberra; National Gallery of NSW, Sydney; Scottish Art Council, Edinburgh; Scottish National Gallery of Modern Art, Edinburgh; Tate, London
The Art Gallery of Ontario, Toronto; The National Gallery of Canada, Ottawa;
Victoria & Albert Museum, London.