From a Cajun family, DesOrmeaux grew up on a farm where he was first introduced to horses through 4-H. He first raced American Quarter Horses and was only sixteen years old when he began working as an apprentice jockey at the Evangeline Downs racetrack in Lafayette, Louisiana. He won his first career stakes race on December 13, 1986, riding Godbey in the Maryland City Handicap at Laurel Park Racecourse.
His immediate success led to him moving north to compete on the Maryland racing circuit in 1987 where his performance earned him the Eclipse Award for Outstanding Apprentice Jockey. In each of his first three years racing in Maryland, Kent DesOrmeaux won more races than any other jockey in the U.S. He is one of only four jockeys to have won three national titles in a row. No longer an apprentice, in 1989, he won the Eclipse Award for Outstanding Jockey and another in 1992. DesOrmeaux, along with Chris McCarron and Steve Cauthen, are the only jockeys to win the Eclipse Award in both the apprentice and overall categories.
In 1989, DesOrmeaux set the current record for most wins in a year with 598. In the early 1990s he moved to southern California and in late 1992 at the Hollywood Park racetrack he was thrown by a horse and trampled, suffering multiple skull fractures and permanent deafness in one ear. Despite the severe setback, he rebounded to his old form, riding Kotashaan to victory in the 1993 Breeders' Cup Turf and at the end of the year his peers voted him the prestigious George Woolf Memorial Jockey Award. In 1995, he scored his second Breeders' Cup title when he beat the "boys" in the Breeders' Cup Sprint with the filly Desert Stormer.
Amongst DesOrmeaux's other major stakes race victories, he became the first foreign jockey to win a Classic race in Japan.
He scored his 5,000th career victory on July 27, 2008 by guiding Bella Attrice to victory in the 7th race at Saratoga Race Course.
In 1998, Kent DesOrmeaux rode Real Quiet to victory in the Kentucky Derby and the Preakness Stakes. DesOrmeaux lost his bid to win the U.S. Triple Crown, and racing immortality, when Victory Gallop beat his horse by a nose in the final stride in the Belmont Stakes. He then went on to ride the Canadian 3-year-old champion colt Archers Bay to victory in the Queen's Plate. In 2000, DesOrmeaux won the Wood Memorial Stakes and his second Kentucky Derby aboard Fusaichi Pegasus.
DesOrmeaux, in 2008, won his third Kentucky Derby aboard Big Brown, in a time of 2:01 4/5. Big Brown won by just under five lengths. DesOrmeaux followed this victory with his ride on Big Brown to victory in the Preakness Stakes at Pimlico Race Course in Baltimore, MD in a time of 1:54 4/5. In the final race of the Triple Crown, however, the Belmont Stakes, DesOrmeaux was forced to ease Big Brown in after the colt tired at the quarter pole. On April 10, 2009, he won the Makers Mark Mile race on Mr. Sidney at Keeneland for a purse of 300,000 dollars.