Cotman was the eldest son of a prosperous silk merchant and lace dealer. His father intended him to go into the family business but instead, intent on a career in art, he moved to London in 1797-98, initially making a living through commissions from print-sellers.
After his death, all of his works and his collection of prints and books were sold by auction at Christie's, realising just over £525 - a relatively paltry sum.
Cotman worked in oils, watercolour, pencil and chalk, and produced many hundreds of etchings. His work can be found in the UK at the Castle Museum and Art Gallery in Norwich (well over 2000 pieces), Tate Gallery, the British Museum and Victoria & Albert Museum in London, the Fitzwilliam Museum in Cambridge, City Art Gallery and other regional centres. In the USA, Cotman is represented at the Yale Center for British Art in New Haven, Connecticut and other galleries around the country.
At 16, Cotman went to London, where he met and studied with J.M.W. Turner, and with him was influenced by Thomas Girtin, master of transparent watercolor painting. Primarily a painter of landscapes and marine views, Cotman also executed numerous prints of architectural antiquities from his native region and from Normandy. For many years he followed in the footsteps of John Crome, teaching and painting in Norwich. In 1834 he was appointed drawing master at King's College, London, a position which he held until his death. Cotman created a fine decorative style of color areas and silhouettes, as in Greta Bridge (c. 1806), which is in the British Museum, London. In his later years he used thickened paints to attain a richer effect.