Born in Chatillon-sur-Seine in France, the son of a metallurgist, Cailletet studied in Paris and then became a manager at his father's foundry.

He is most famous for his work on the liquefaction of gases. Cailletet realized that the failure of others to liquefy the permanent gases, even under enormous pressures, was explained by Thomas Andrews's concept of critical temperature. In 1877 he succeeded in producing liquid oxygen by allowing the cold, compressed gas to expand. This technique, depending on the effect discovered by Joule and Thomson, cooled the gas to below its critical temperature. In later experiments he liquefied nitrogen and air. Raoul Pictet, working independently, used a similar technique. In 1884 Cailletet was elected to the Paris Academy for his work. He is also the inventor of the altimeter and the high-pressure manometer.