Jack LeGoff was born in France in 1931 and competed in dressage, show jumping, and eventing as a child, even riding steeplechasers as a teenager. He joined the French military in 1948 and began riding for Cadre Noir, the national riding academy. LeGoff was the French National Eventing Champion in 1956 and first competed for France at the 1960 Olympics where he earned a team bronze medal and placed sixth individually. After serving in the Algerian War he represented France again at the 1964 Olympics.
After coaching the French eventing team at the 1968 Olympics he was recruited to coach the USET three-day event team. From 1970 to 1984, the time during which LeGoff coached the team, the United States is said to have experienced the "Golden Age" of eventing and the USET earned an unprecedented 18 medals in international competition:
After retiring from coaching the U.S. Olympic Team in 1984, he consulted for the USET identifying and developing riders, served as Director of the USET Training Center, and coached the 1992 Canadian Olympic Team. In 1996, LeGoff judged the Olympic Three-Day Event in Atlanta and served as a FEI judge at other events around the world.
LeGoff was not only a brilliant coach of international teams but took the time to study the grassroots riders, attending not only the top-level competitions but those at the lower levels as well. He conducted clinics that were open to the public and assisted with USPC rallies.
Denny Emerson, who rode under LeGoff on the 1974 gold medal World Championship team, called him the "winningest" coach. Writing in The Chronicle of the Horse, Emerson stated, "Right now, and I'd bet for years to come, the LeGoff dynasty will remain the gold standard against which people will measure any other USET three-day team.”