The son of a gentry family from the Gascony region, Gustave Lassalle-Bordes went to Paris to study painting, particularly historical painting.
He exhibited in the official Salons and worked with Charles Larivière, a historical painter, and with Jules Claude Ziegler, then working on the wall paintings for the Madeleine church in Paris. Through them, he learned to be an excellent painter "in the manner of" the artist for whom he was working. Starting in 2838, he joined Delacroix’s studio on rue Neuve-Guillemin, where he ran the studio until 1846; he helped the master decorate the wall paintings for the libraries of the Palais Bourbon and the Senate. But in 1848, his relationship with the master deteriorated: he told Philippe Burty of his work with Delacroix and about the master’s techniques, speaking with interest but in the demanding and bitter way of someone who has been working in the shadows.
He then returned to Auch. Flush with his collaboration with Delacroix, the medals he was awarded at the Salons, and flattering reviews - notably from Baudelaire in the 1846 Salon - he received many commissions from churches and châteaux in the region. He died in Auch in 1886.