Born to an impoverished Irish smallholder in 1725, O'Kelly moved to London as a young man, where he worked as a sedan chair carrier. There he is reputed to have duped a wealthy heiress into marrying him, and absconded with her inheritance of £1,000; elsewhere this tale is dismissed as hearsay and the source of his initial wealth attributed to gambling. Either way, his money was soon frittered away on drink and gambling. This led in 1756 to a stay in the Fleetdebtors' prison, where he met prostituteCharlotte Hayes. O'Kelly and Hayes formed a business, if not romantic, partnership which persisted for the rest of their lives. Both were freed in 1760 as part of George III's amnesty for those in debtor's jails. O'Kelly plied his trade as a conman in London's coffee-houses and, through his gambling contacts, introduced clients to Hayes. It is reported that O'Kelly himself took in female clients. Within eight years, they had amassed a total of £40,000, enough to branch out into racehorse ownership. They also came to own a significant property portfolio, including Clay Hill estate outside of Epsom, Cannons Park, a substantial villa built by William Hallett Esq, and former estate of the Duke of Chandos in Stanmore, Middlesex also property in Piccadilly and Half Moon Street in London O'Kelly began to learn about horse racing and breeding from some of the visitors to Hayes' establishment. It was here, from one of Hayes' clients, that he heard about a stallion bred by the late Duke of Cumberland, named Eclipse, of whom he purchased a 1/8th share.
Eclipse
In 1769, his first season as a racehorse, the five-year-old Eclipse had remained unbeaten in the nine races he contested. This inspired O'Kelly to buy the horse outright from his owner William Wildman for the sum of 1,100 guineas. In 1770, under O'Kelly's ownership, Eclipse remained unbeaten for another nine races and retired having won career prize money of £3,000. Eclipse then went to stud for a fee of 50 guineas, the highest stud fee in the country, where he sired 930 colts and fillies over 17 years. Amongst the best of them were Young Eclipse and Serjeant, who enhanced Eclipse's stud reputation by winning early renewals of the Derby under O'Kelly's ownership. O'Kelly had narrowly missed out on winning the very first Derby with another son of Eclipse, Boudrow. Success with horses brought O'Kelly wealth, but not social standing. The Jockey Club refused his membership, even after O'Kelly became a Captain and then Lieutenant-Colonel in the Middlesex Militia. Despite his social ascent, and obvious charisma, the evidence of his humble upbringing remained:
Death
O'Kelly died of gout in 1787. He died "at about his sixty-seventh year of age", which would cast doubt on the accuracy of his birth date. His will stated that all his racehorses should be sold off and that his brother Philip and nephew Andrew should forfeit £500 of their inheritance if they retained any involvement in racehorses. It is said he was:
