Dr. St. Louis was born and raised in New England, the second of six children.  He attended secondary school at Phillips Academy, Andover, and did his undergraduate studies at Harvard College.  There he majored in Biology, and graduated Cum Laude in 1980.  During his career at Harvard, he did research at the Scripps Research Foundation (San Diego) in the Department of Cellular Biology  where he helped develop a novel procedure for isolating DNA-cleaving enzymes. He also spent a summer as a stagiaire de formation (general internship) at the Centre Medicalle de Forcilles near Paris, France. He earned his varsity letter in swimming as a springboard diver.

Dr. St. Louis attended  the University of Massachusetts Medical School where he graduated second in his class in 1984. While attending medical school, he did independent clinical research in Seattle, and published three peer-reviewed journal articles in the fields of cardiology and emergency medical services (cardiopulmonary resuscitation). He also married his college sweetheart, Robin.

In the summer of 1984, Dr. St. Louis left the northeast and moved to Los Angeles where he completed his internship and residency in Internal Medicine at the UCLA Medical Center. There, he was among a select group of 12 doctors who participated in the General Internal Medicine specialization tract, which offered exposure to office-based disciplines (such as orthopedics, dermatology, gynecology, neurology, pain management) in addition to traditional intensive adult-medicine training.

After residency training, Dr. St. Louis was recruited to join  the Sansum Medical Clinic in Santa Barbara, California. He practiced at the Clinic for three years, enjoying staff privileges at the Santa Barbara Cottage Hospital and appointment to the Clinical Faculty of the USC School of Medicine.

In 1990, Dr. St. Louis elected to move from the coast to the desert in order to open a solo practice of Internal Medicine. He has been proudly associated with the Eisenhower Medical Center ever since, having served as chairman of both the hospital's Institutional Review Board and Pharmacy and Therapeutics committee. In 2003, Dr. St. Louis shifted the scope of his practice to create the desert's first dedicated boutique-style  practice.

Dr. St. Louis resides in Palm Desert with his wife and two children, Andy and Carrie. He is active with the Desert Bicycle Club, and can be seen pedaling more than 100 miles per week around Valley streets. When not on the bike, he "relaxes" on the golf course, diligently trying to maintain his single-digit handicap.