Carnot came from a distinguished Parisian political family; his father, Lazare, was a leading politician under Napoleon Bonaparte. He studied at the Ecole Polytechnique, from which he graduated in 1814. For the next few years he worked as a military engineer, but the political climate had changed with the fall of Bonaparte and, in 1819, he transferred to Paris and concentrated on scientific research.

The fruits of this work ripened in 1824 in the form of a book called Réflexions sur la puissance motrice de feu (On the Motive Power of Fire). The main theme of this masterpiece was an analysis of the efficiency of engines in converting heat into work. He found a simple formula depending only on the temperature differences in the engine and not on intermediate stages through which the engine passed. He also introduced the concept of reversibility in the form of the ideal Carnot cycle. Using these ideas he derived an early form of the second law of thermodynamics, stating that heat always flows from hot to cold. It became an inspiration, many years later, for Rudolf Clausius's formulations of thermodynamics. Carnot died of cholera at the age of 36.