The son of a Bordeaux accountant and a creole mother, he met in high school the future poet Francis Jammes and Gabriel Frizeau the legendary art collector. He taught himself to paint and from 1894 to 1897 he made several important contacts: André Gide, Arthur Fontaine, the brothers Rouart and the composer Henri Duparc.
His frequent stays in London marked his vision of the nature of a hazy melancholy. He was refused at the Society of Friends of the Arts in Bordeaux, but appeared in public in 1898 at the Salon de La Plume, a magazine then published his article "Simplicity in Painting" and then he exhibited in October at the Salon des Cent.
He moved to Paris and from 1901 to 1914 exhibiting at the Salon des Independents. He was a founding member of the Salon d'Automne, he also exhibited at the Salon of Free Aesthetics in Brussels in 1907 and Salon of the Golden Fleece of Moscow in 1908.
By a process of simplification and a kind of desired naivety, Lacoste, faithful to the idealistic tendency, found subjects of wonder or reverie sometimes disturbing in the foggy and wintry atmospheres which allow the artist to simplify the forms.
Charles Lacoste lived in Monein, then in Pardies, where a street and the communal primary school bear his name. He is buried in the cemetery of Pardies.