A chestnut thoroughbred, Secretariat was foaled at Christopher Chenery's Meadow Stable, near Doswell, Virginia, on March 30, 1970. Nicknamed "Big Red" (like the legendary thoroughbred Man o' War), he developed into a beautiful and powerful horse, with a heart more than twice the size of a standard horse and massive chest and hindquarters. He had good breeding; his sire, Bold Ruler, had won the 1957 Preakness Stakes, and his dame, Something Royal, was a daughter of Princequillo.

Bred and owned by Chenery's daughter, Penny Tweedy, trained by Lucien Laurin, and ridden by Ron Turcotte, Secretariat won several notable stakes races as a two-year-old, which earned him both the Eclipse Award as the best two-year-old and Horse of the Year honors. He became the odds-on favorite to win the Triple Crown, something that had not been done since Citation in 1948. He began his remarkable journey with a record-setting performance in the Kentucky Derby, eclipsing both the track and race records for the mile-and-a-quarter. Remarkably, his times for each quarter were progressively faster. He followed this achievement with another victory in the Preakness, falling just short of the race record, although there was some controversy over his race time. Sham was the runner-up in both races.

At the final race in the Triple Crown, the arduous mile-and-a-half Belmont Stakes, Secretariat stunned the racetrack crowd and television viewers alike with what Sports Illustrated writer Whitney Tower called "the greatest performance by a racehorse in this century." He won by an amazing thirty-one lengths over Twice a Prince in a time of 2:24, the fastest mile-and-a-half ever run on a dirt track.

At a time when the news was still focused on the Vietnam War (1956–1975), Secretariat's exploits captured Americans' imaginations. He appeared on the covers of Time, Newsweek, and Sports Illustrated, and repeated his accolades as horse of the year. As sports columnist Pete Axthelm wrote in Newsweek magazine in 1973, "Secretariat generates a crackling tension and excitement wherever he goes … [His] muscular build identifies him immediately, his glowing reddish coat is a banner of health and rippling power. Magnificent enough at rest … when he accelerates … he produces a breathtaking explosion that leaves novices and hardened horsemen alike convinced that, for one of those moments that seldom occur in any sport, they have witnessed genuine greatness."

Secretariat won and lost a few more races, setting more records in the process, and after his final race on October 28, 1973, he was retired to stud in Paris, Kentucky. He had won sixteen of twenty-one races, most by handsome margins, and accumulated $1.3 million in winnings over his career. He sired many foals, including stakes winners, but none of them matched his reputation. He died at Claiborne Farm, Paris, Kentucky, in 1989.