As a professor at the Harvard School of Public Health, Mayer directed a laboratory that did groundbreaking work on the hypothalamic regulation of obesity and various metabolic disorders.

Jean Mayer's sister, Dr. Geneviéve Massé would become a Professor of Biostatistics at the French National Superior School of Public Health.

Mayer worked in his father's laboratory as a schoolboy, while devoting the greater part of his intellectual energies to mathematics—differential and integral calculus, analytical geometry, series and functions, and theoretical physics.

A Free French sympathizer with a high position in the Vichy government secretly supplied him with a passport and papers permitting his escape to Algeria, Morocco, Martinique and Guadeloupe.

He would eventually make his way to the United States, where his father, who immediately before the outbreak of war had been invited to give the Lowell Lectures at Harvard, was in Cambridge, Massachusetts, with Mayer's mother and sister.

[3] In North Africa, Mayer served as commander of an artillery battery in the Colonial and Marine First Free French Division that accompanied the British Eighth Army at the second battle of El Alamein, following its victory there with a long advance into Libya and Tunisia.

After the D-Day landings, he would land in the south of France to command a Free French infantry regiment—made up largely of boys too young to have been drafted for forced labor in Germany and older men who had served in World War I—in the Colmar Pocket, managing to hold the line along the Vosges against attack by the elite Hermann Goering SS Division.

[4] At war's end, Mayer joined his wife in the United States and received a small grant from the Rockefeller Foundation for graduate work in physiological chemistry.

The salary of eighteen hundred dollars turned out to be crucial to his household income when his first son, André, the first of five Mayer children, was born in 1946.

)[6] This basic insight would lead, after many more years of research and experimentation, to Mayer's greatest contribution: the so-called glucostatic theory of the regulation of food intake.

During his Harvard years, he would serve as a consultant to the World Health Organization and UNICEF, as the head of a United Nations Task Force on Child Nutrition, as Chair of the U.S. National Council on Hunger and Malnutrition in the U.S.(1968–69)—the now-familiar Food Stamps program would emerge from the Council's findings—Chairman of the First White House Conference on Food, Nutrition, and Health (1969–70), and adviser to many foundations, community action organizations, and scientific societies.

He would also become a public voice on "popular" health and nutrition issues, writing a syndicated column that appeared twice weekly in 100 of the largest newspapers in the United States, with a combined circulation of 35 million readers.

Mayer is remembered as having brought with him a sense of energy and excitement, playing a leading role in the development of internal "house courses," with classes for Dudley students taught by faculty members of its Senior Common Room, bringing in personal friends such as Daniel Patrick Moynihan and George McGovern as after-dinner speakers at House dinners, and adding faculty from Harvard Medical School and the Harvard School of Public Health to a Senior Common Room already containing as longtime members such Arts and Sciences faculty as philosopher Nelson Goodman, sociologist Seymour Martin Lipset, physicist Robert Pound, ethnobotanist Richard Evans Schultes, legal scholar Roger Fisher, and topologist Arthur Lee Loeb, who would later succeed John Mayer as Master of Dudley.

The House became during Mayer's mastership — remembered for the outstanding Dudley symposium series,[9] folk and jazz concerts, readings by such poets and authors as Anne Sexton and John Updike,[10] a pioneering Film Society whose showings of rare and classic films drew students from across campus,[11] dance recitals and small-cast theatrical productions — a vital center of undergraduate life.

He represented a style of American college and university presidents who were becoming increasingly rare: the genuine academic leader, in charge of the intellectual enterprise from start to finish.