The Moon and Sixpence (1919) by W. Somerset Maugham
This lovely novel by Maugham (who also wrote the autobiographical masterpiece Of Human Bondage ) takes its inspiration from the life of French artist Paul Gauguin. Charles Strickland, a middle-aged English stockbroker, decides one day to abandon his banal life in order to devote himself to painting. Leaving his wife and career for an unknown future, Strickland embraces an existence fully devoted to creativity, and while his abrupt renunciation of his past life may seem callous, his courage to pursue something socially deemed "impractical" for something he loves is also inspiring.
And if you're into novels about painters, also see Émile Zola's The Masterpiece (1886), which is based on the life of Paul Cézanne.