On November 17th 1910, Gaston Haag married the daughter of Pierre Theophile Thomas, Aline Augustine Suzane, born in Paris 9° on January 9 1883. His brother, Maurice, home designer, was his wedding best boy.
Gaston Haag painted his firsts artworks in 1896 but never exhibited them in any Salon de Paris. The Ecouen City Hall owns one, “Promeneur dans le bois d’Ecouen” (hiker in the Ecouen woodland).
Gaston Haag donated one of his paintings to the Ecouen city council.
After his death, his widow sent a bitter letter to the City of Ecouen officials, saying: “My father in law, my father and my husband gave several of their paintings to the City Hall. I would never have thought that the Mayor would have let down the daughter and widow of these gentlemen”.