Bred by Mr. Halford, Leamington had excellent conformation. He was not only a fast horse, but also showed great staying ability. Halford began racing him at age two, and then sold the to a Mr. Higgins. Leamington won the Woodcote Stakes at Warwick and the Chesterfield Stakes, before being retired for the year.
As a three-year-old, it was planned to run the colt in the Epsom Derby, but he contracted strangles, and this affected his whole three-year-old season. However, his owners and trainers appeared to have planned his losses to help keep his handicap weight down. After losing four small races carrying little weight, he won the Wolverhampton, before his losing several more. He was then "allowed" to win the Stewards' Cup carrying only 98 lb (44 kg).
His four-year-old career began with the 2.25 mile Chester Cup. Leamington only carried 93 lb (42 kg), due to his poor reputation gained as a three-year-old, and he easily won the race. The colt then came fourth at the Ascot Gold. He went on to the Goodwood Stakes, carrying only 118 lb (53.5 kg) with odds of 100 to 3, and easily won the race by a length. His owners won quite a bit of money from wagering on him that day, after their longshot with 100 to 3 odds beat out a field of 19. However, his win earned him top weight of 131 lb (59 kg) at his next race, the Chesterfield Cup, and he could not hold out.
Leamington ran once at the age of five. He carried 130 lb (59 kg), as the handicapper realized how the horse's owners had been manipulating his races. The weight was too much to take, and Leamington could not hold out here either. He had a successful start to his six-year-old career, however, winning the Chester Cup easily against a tough field. He finished second in his next race, the Queen's Gold Vase at Ascot, but his final race of the season, the Goodwood Cup, left him with an injury to his right foreleg.
He began training in 1860 as a seven-year-old for The Whip Stakes, a strenuous four-mile race. He broke down while preparing, and was retired to begin his breeding at Rawcliffe Paddocks.
Cameron then sent the stallion to his own Clifton Stud on Staten Island. He was then moved to New Jersey in 1868, before being shipped to Annieswood Farm in 1871. His offspring were now noted for their fantastic speed, including the famous colt, Aristides, the winner of the first Kentucky Derby.
Leamington was sold to Aristides Welch, who stood the stallion at his Erdenheim Stud, near Philadelphia, Pennsylvania. Leamington finished out his life here, dying on May 6, 1878 at the age of 25. During his breeding career, he was the leading sire in America four times, including beating out the great horse Lexington in 1875 for the first time in 16 years. He also earned this title in 1877, 1879, and 1881.