Monod was born in Paris, and graduated from the university there in 1931; he became assistant professor of zoology in 1934, having spent the years immediately following his graduation investigating the origin of life. After World War II, in which he served in the Resistance, he joined the Pasteur Institute, becoming head of the cellular biochemistry department in 1953.

In 1958 Monod began working with François Jacob and Arthur Pardee on the regulation of enzyme synthesis in mutant bacteria. This work led to the formulation, by Monod and Jacob, of a theory explaining gene action and particularly how genes are switched on and off as necessary. In 1960 they introduced the term ‘operon’ for a closely linked group of genes, each of which controls a different step in a given biochemical pathway. The following year they postulated the existence of a molecule, messenger RNA, that carries the genetic information necessary for protein synthesis from the operon to the ribosomes, where proteins are made. For this work Monod and Jacob were awarded the 1965 Nobel Prize for physiology or medicine, which they shared with André Lwoff, who was also working on bacterial genetics.

In 1971 Monod became director of the Pasteur Institute and in the same year published the best-selling book Chance and Necessity, in which he argued that life arose by chance and progressed to its present level as a necessary consequence of the pressures exerted by natural selection.