He was born on 26 August 1850 in Paris the son of Alfred Richet. He was educated at the Lycee Bonaparte in Paris then studied Medicine at university in Paris.

Richet held a deep interest in extrasensory perception and hypnosis. In 1884, Alexandr Aksakov interested him in the medium of Eusapia Palladino. In 1891, Richet founded the Annales des sciences psychiques. He kept in touch with renowned occultists and Spiritualists of his time such as Albert von Schrenck-Notzing, Frederic william Henry Myers and Gabriel Delanne. In 1919, Richet became honorary chairman of the Institut Métapsychique International in Paris, and, in 1930, full-time President.

In 1887, Richet became professor of physiology at the Collège de France investigating a variety of subjects such as neurochemistry, digestion, thermoregulation in homeothermic animals, and breathing. In 1898, he became a member of the Académie de Médecine. In 1913, his work with Paul Portier on anaphylaxis the term he coined for a sensitized individual's sometimes lethal reaction to a second, small-dose injection of an antigen won the Nobel Prize in Physiology or Medicine. The research helped elucidate hay fever, asthma and other allergic reactions to foreign substances and explained some previously not understood cases of intoxication and sudden death. In 1914, he became a member of the Académie des Sciences.

Richet with Oliver Lodge, Frederic W. H. Myers and Julian Ochorowicz investigated the medium Eusapia Palladino in the summer of 1894 at his house in the Ile Roubaud in the Mediterranean. Richet claimed furniture moved during the séance and that some of the phenomena was the result of a supernatural agency. However, Richard Hodgson claimed there was inadequate control during the séances and the precautions described did not rule out trickery. Hodgson wrote all the phenomena "described could be account for on the assumption that Eusapia could get a hand or foot free." Lodge, Myers and Richet disagreed, but Hodgson was later proven correct in the Cambridge sittings as Palladino was observed to have used tricks exactly the way he had described them.

In the British Medical Journal on 9 November 1895 an article was published titled Exit Eusapia!. The article questioned the scientific legitimacy of the SPR for investigating Palladino a medium who had a reputation of being a fraud and imposture. Part of the article read "It would be comic if it were not deplorable to picture this sorry Egeria surrounded by men like Professor Sidgwick, Professor Lodge, Mr. F. H. Myers, Dr. Schiaparelli, and Professor Richet, solemnly receiving her pinches and kicks, her finger skiddings, her sleight of hand with various articles of furniture as phenomena calling for serious study." This caused Henry Sidgwick to respond in a published letter to the British Medical Journal, 16 November 1895. According to Sidgwick SPR members had exposed the fraud of Palladino at the Cambridge sittings, Sidgwick wrote "Throughout this period we have continually combated and exposed the frauds of professional mediums, and have never yet published in our Proceedings, any report in favour of the performances of any of them." The response from the Journal questioned why the SPR wastes time investigating phenomena that are the "result of jugglery and imposture" and not urgently concerning the welfare of mankind.

In 1898, Myers was invited to a series of séances in Paris with Richet. In contrast to the previous séances in which he had observed fraud he claimed to have observed convincing phenomena. Sidgwick reminded Myers of Palladino's trickery in the previous investigations as "overwhelming" but Myers did not change his position. This enraged Richard Hodgson, then Editor of SPR publications to ban Myers from publishing anything on his recent sittings with Palladino in the SPR journal. Hodgson was convinced Palladino was a fraud and supported Sidgwick in the "attempt to put that vulgar cheat Eusapia beyond the pale." It wasn't until the 1908 sittings in Naples that the SPR reopened the Palladino file.

He was involved in the French pacifist movement. Starting in 1902, pacifist societies began to meet at a National Peace Congress, often with several hundred attendees. Unable to unify the pacifist forces they set up a small permanent delegation of French Pacifist Societies in 1902, which Richet led, together with Lucien Le Foyer as Secretary-General.

In 1905, Eva Carrière held a series of séances at Villa Carmen and sitters were invited. In these séances she claimed to materialize a spirit called Bien Boa a 300-year-old Brahmin Hindu, however, photographs taken of Boa looked like the figure was made from a large cardboard cutout. In other sittings Richet reported that Boa was breathing, had moved around the room and had touched him, a photograph taken revealed Boa to be a man dressed up in a cloak, helmet and beard.

A newspaper article in 1906 had revealed that an Arab coachman known as Areski who had previously worked at the villa had been hired to play the part of Bien Boa and that the entire thing was a hoax. Areski wrote that he made his appearance into the room by a trapdoor. Carrière had also admitted to being involved with the hoax.

Richet was a proponent of eugenics, advocating sterilization and marriage prohibition for those with mental disabilities. He expressed his racist and eugenist ideas in his 1919 book La Sélection Humaine. From 1920 to 1926 he presided over the French Eugenics Society.

Richet's works on parapsychological subjects, which dominated his later years, include Traité de Métapsychique (Treatise on Metapsychics, 1922), Notre Sixième Sens (Our Sixth Sense, 1928), L'Avenir et la Prémonition (The Future and Premonition, 1931) and La Grande Espérance (The Great Hope, 1933).

He hypothesized a “sixth sense”, an ability to perceive hypothetical vibrations, which he discussed in his 1928 book Our Sixth Sense. Although he believed in extrasensory perception, Richet did not believe in life after death or spirits.

In 1954, the Society for Psychical Research member Rudolf Lambert published a report revealing details about a case of fraud that was covered up by many early members of the Institut Métapsychique International (IMI). Lambert who had studied Gustav Geley's files on the medium Eva Carrière discovered photographs depicting fraudulent ectoplasm taken by her companion Juliette Bisson. Various "materializations" were artificially attached to Eva's hair by wires. The discovery was never published by Geley. Eugéne Osty (the Director of the institute) and members Jean Meyer, Albert von Schrenck-Notzing and Richet all knew about the fraudulent photographs but were firm believers in mediumship phenomena so demanded the scandal be kept secret.