Jean Léonard Marie Poiseuille^{[lower-alpha 1]} (French: [pwazœj]; 22 April 1797^[3] – 26 December 1869) was a French physicist and physiologist.

Poiseuille was born in Paris, France, and he died there on 26 December 1869.^[4]

From 1815 to 1816 he studied at the École Polytechnique in Paris. He was trained in physics and mathematics.^[5] In 1828 he earned his D.Sc. degree with a dissertation entitled Recherches sur la force du coeur aortique (The force of the aortic heart). He was interested in the flow of human blood in narrow tubes, and invented the U-tube mercury manometer (or hemodynamometer) to measure arterial blood pressures in horses and dogs.^[4]

In 1838 he experimentally derived, and in 1840 and 1846 formulated and published, Poiseuille's law (now commonly known as the Hagen–Poiseuille equation, crediting Gotthilf Hagen as well), which applies to laminar flow, that is, non-turbulent flow of liquids through pipes of uniform section, such as blood flow in capillaries and veins. The poise, the unit of viscosity in the CGS system, was named after him.