[9][10][11] Mary Katharine Ralph was born April 1, 1939, in New Brunswick, New Jersey,[1] and grew up in Painesville, Ohio, where her father taught history at Lake Erie College.

Her physics professor, Dorothy Montgomery, helped her to find work in the Louis Leprince-Ringuet laboratory in France during a year abroad, and at Brookhaven National Labs in the summer.

[13] At the end of her first year at Columbia she married Jean-Marc Gaillard, a visiting physics postdoctoral student.

She moved with him, first to the University of Paris at Orsay, France and a year later to the European Organization for Nuclear Research (CERN) in Geneva, Switzerland.

[1] In 1979 Gaillard established a particle theory group at the Laboratoire d'Annecy-le-Vieux de physique des particules (LAPP), Annecy-le-Vieux, France.

[1] She was concurrently a faculty senior staff member at Lawrence Berkeley National Laboratory (LBNL), where she headed the Theory Group from 1985 to 1987.

Her later work focused on effective supergravity theories based on superstrings, and their implications for phenomena that may be detected both in accelerator experiments and cosmological observations.