Richet, the son of a distinguished Parisian surgeon, studied medicine at the University of Paris. After graduation in 1877 he worked at the Collège de France before he returned to the University of Paris where he served as professor of physiology from 1887 until his retirement in 1927.

Richet worked on a wide variety of problems, which ranged from heat regulation in mammals to the unsuccessful development of an anti-TB serum. His most important work began, however, with his investigation of how dogs react to the poison of a sea anemone. He found that he could induce a most violent reaction in dogs that had survived an original injection without any distress. If 22 days later he gave them a second injection of the same amount then they immediately became extremely ill and died in 25 minutes. Richet had discovered the important reaction of anaphylaxis, a term he coined in 1902 to mean the opposite of phylaxis or protection.

By 1903 he was able to show that the same effect could be produced by any protein whether toxic or not as long as there was a crucial interval of three to four weeks between injections. His work was to have profound implications for the newly emerging science of immunology and gained for Richet the 1913 Nobel Prize for physiology or medicine.