Jeanloz attended Collège Calvin, where he pursued Greek and Latin classical studies, graduating with a bachelor's of science in 1936.
Five years later, Jeanloz completed a diploma in chemical engineering from the University of Geneva, specializing in organic chemistry and biochemistry.
Jeanloz worked for Tadeusz Reichstein from 1944 to 1946, when he moved his postdoctoral research overseas, with a year each at the University of Montreal in Canada and National Institutes of Health in the United States.
In 1961, Jeanloz was named head of the Laboratory for Carbohydrate Research at Mass General, and as an undergraduate adviser at Harvard College.
Harvard Medical School appointed Jeanloz a professor of biological chemistry and molecular pharmacology in 1969, and granted him emeritus status in 1988.