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Gay-Lussac was the son of a judge who was later imprisoned during the French Revolution. Born at St. Léonard in France, he entered the recently founded Ecole Polytechnique in 1797 and graduated in 1800. His career was thereafter one of steady promotion. Originally studying engineering, in 1801 he attracted the attention of the chemist Claude-Louis Berthollet who made him his assistant at Arcueil, near Paris. The science of chemistry was then in its infancy. Few chemists were actively engaged in research, and the equipment used was primitive. Chemical symbols had just been introduced, and no chemical formulae were known with certainty. During his career Gay-Lussac contributed to the advancement of all branches of chemistry by his discoveries, and greatly improved and developed experimental techniques.

In 1802, following the researches of the chemist Jacques Charles, Gay-Lussac formulated the law now alternatively attributed to himself and Charles – that gases expand equally with the same change of temperature, provided the pressure remains constant. By using superior experimental techniques, Gay-Lussac largely eliminated the errors of his predecessors in this field, in particular by developing a method of drying the gases. He measured the coefficient of expansion of gases between 0°C and 100°C, thus forming the basis for the idea of the absolute zero of temperature. His law was received with satisfaction as complementary to Boyle's law. It was later shown that Gay-Lussac's and Boyle's laws applied exactly only to a hypothetical ‘ideal gas’; real gases obey the law approximately.

Gay-Lussac made his first daring balloon ascent in 1804 with Jean Biot, during which they made scientific observations and established that there was no change in either the composition of the air or in the Earth's magnetic force at the heights they reached. Gay-Lussac made a second ascent alone, reaching a height of 23,018 feet.

In 1805, by exploding together given volumes of hydrogen and oxygen, Gay-Lussac discovered that one volume of oxygen combined with two volumes of hydrogen to form water. In 1808, after researches using other gases, he formulated his famous law of combining volumes – that when gases combine their relative volumes bear a simple numerical relation to each other (e.g., 1:1, 2:1) and to the volumes of their gaseous product, provided pressure and temperature remain constant. The English chemist John Dalton was immediately interested in Gay-Lussac's discovery, but when, on investigation, the law appeared to conflict with his own theory of the indivisibility of atoms, Dalton rejected the law and sought to discredit Gay-Lussac's experimental methods. The reason for the apparent conflict was that the difference between an atom and a molecule was not clearly understood, and it was left to the Italian chemist Amedeo Avogadro to formulate a theory reconciling the two laws, thus laying the basis of modern molecular theory.

From 1808 Gay-Lussac worked with the chemist Louis Thenard. Following Humphry Davy's isolation of minute amounts of sodium and potassium, the two chemists in 1808 prepared these metals in reasonable quantities. It was during his experiments with potassium as a reagent that Gay-Lussac blew up his laboratory, temporarily blinding himself. In collaboration with Thenard he isolated and named the element boron. Simultaneously with Davy, Gay-Lussac investigated in 1813 a substance first isolated by Bernard Courtois and established that it was an element similar to chlorine. He named it iodine from the Greek ‘iode’ meaning violet. In 1815 he prepared cyanogen and described it as a compound radical. He proved that prussic acid (hydrogen cyanide) was made up of this radical and hydrogen, completing the overthrow of Lavoisier's theory that all acids must contain oxygen. His recognition of compound radicals laid the basis of modern organic chemistry.

Gay-Lussac also investigated fermentation, the phenomenon of supercooling, the growth of alum crystals in solution, the compounds of sulfur, and the various stages of oxidation of nitrogen. With the young student Justus von Liebig he investigated the fulminates. In his later years he improved on experimental techniques, and laid the basis of modern volumetric analysis.

In 1827 he devised the Gay-Lussac tower. Oxides of nitrogen arising from the preparation of sulfuric acid by the lead-chamber process, which formerly escaped into the atmosphere, are absorbed by passing them up a chimney packed with coke, over which concentrated sulfuric acid is trickled. This tower and its modifications are used in many chemically-based industries today.

Gay-Lussac was a chemist of brilliance and determination. Although said to be cold and reserved as a man, as a researcher he was bold and energetic. Shortly before his death he expressed regret at the experiments that he would never be able to perform.