Westall was apprenticed to a heraldic silver engraver in 1779, where he was encouraged to become a painter by John Alefounder;[1] he then began studying at the Royal Academy School of Arts from 10 December 1785.

From 1790 to 1795 he shared a house with Thomas Lawrence (later Sir), the future Royal Academy president, at 57 Greek Street, on the corner of Soho Square, each of the artists placing their name on one of the entrances.

His works – many in watercolour – caused great interest in the late years of the 18th century when he was considered by his chief patron Richard Payne Knight to be an outstanding artist of the picturesque.

A number of scenes in which Westall depicts events in the life of Horatio Nelson are at the National Maritime Museum.

Westall was a prolific book illustrator of both fiction and poetry, including the works of Sir Walter Scott, Oliver Goldsmith, William Cowper and Thomas Gray.