He founded the Chilean National Museum of Natural History, its first director was another Frenchman Jean-François Dauxion-Lavaysse.

[3] Gay first went to Paris to study medicine, but he quickly abandoned this idea to become a researcher in natural history.

After having visited Peru in 1839, he lived in Santiago, where he wrote the multi-volume Historia fisica y politica de Chile.

[4] At the end of 1858, he was sent by the French Academy of Sciences to study the mining system of the United States.

He is commemorated in the name of a number of plants and animals, including the flower Montiopsis gayana and the rufous-bellied seedsnipe Attagis gayi.