Mary Hewitt was born on April 28, 1899 in Clovis, California. Her parents, who were British, had migrated to the United States from England to escape an economic depression.[1] She earned a Bachelor of Arts in biology at Stanford University in 1921, supporting herself by working as a waitress and a secretary.[1][2] She then began a Doctor of Medicine at Stanford as one of only two women in her class and graduated in 1925.