Perey, the daughter of an industrialist, was born at Villemomble in France and educated at the Faculté des Sciences de Paris. She began her career in 1929 as an assistant in the Radium Institute in Paris under Marie Curie. In 1940 she moved to the University of Strasbourg, becoming professor of nuclear chemistry in 1949 and director of the Center for Nuclear Research in 1958.

By the 1930s chemists had discovered all the elements of the periodic table below uranium except for those with atomic numbers 43, 61, 85, and 87. Many claims had been made for the discovery of element 87 with it being variously and prematurely named russium, moldavium, and virginium. In 1939 Perey found in the radioactive decay of actinium–227 the emission of alpha-particles as well as the expected beta-particles. As an alpha-particle is basically a helium nucleus with an atomic mass of 4 this implied that Perey had discovered a nuclide of mass number 223. Further investigation showed it to be one of the missing elements, with an atomic number of 87. She originally called it actinium K but in 1945 named it francium (for France).