The daughter of a schoolteacher, Marguerite Hazard-Bar belonged to a literate family. In 1908, she married Augustin Bar, at that time a dealer in objets d’art.
In 1919, the couple separated and Marguerite Hazard-Bar was awarded custody of their three children. He had to provide for them. She joined the Combined Faculty of Medicine and Pharmacy in 1920, becoming the institution’s first female ‘lab boy’.
Recognised for her professionalism, she first worked with Jean Minet, a professor of therapeutics, before joining the hydrology laboratory run by Professor Émile Duhot in 1929 until her retirement in 1944.
She didn’t go to university, unlike her brothers, all of whom went on to have brilliant careers: Paul, a professor of literature and member of the Académie Française, Jean, a mechanical engineer in the French Navy, and René, a physiologist and pharmacologist and member of the Académie de Médecine.