Born in London, Luny became Francis Holman's pupil and assistant, staying with him for many years. In a style and coloration which were much brighter and warmer than Holman's, Luny found popular success with his portraits and narrative scenes, painting nearly 3000 paintings over the course of his life.
In addition to painting, he served in the French Revolutionary wars as a purser in the royal navy serving under Captain George Tobin. With this accountant mind, the artist kept similar records of all works painted, including paintings' titles, purchaser's names and prices paid.
Indomitable in spirit, in his later years he was handicapped by severe rheumatoid arthritis yet he continued to paint prodigiously with brushes strapped to his wrists. He exhibited with the Royal Academy and the City Art Gallery of Bristol.