[5] His father, Anthony Gay, son of a doctor, was a lawyer and prosecutor and worked as a judge in Noblat Bridge.

Three years later, Gay-Lussac transferred to the École des Ponts et Chaussées, and shortly afterward was assigned to C. L. Berthollet as his assistant.

In 1804 he was appointed répétiteur (demonstrator) to Antoine François Fourcroy at the École Polytechnique, whom he succeeded in 1809 as professor of chemistry.

He had first met her when she worked as a linen draper's shop assistant; he noticed she was studying a chemistry textbook under the counter, which led to their acquaintance.

Gay-Lussac had a reputation as one of the greatest European scientists of his day, well justified by his innumerable discoveries in both chemistry and physics.