His first ride in the National was aboard Glenkiln, the lesser fancied of two horses owned by Noel Le Mare, in 1973. Glenkiln fell at the Chair, while his stable companion, Red Rum, ridden by Brian Fletcher, pulled off a dramatic, last-gasp victory over the gallant Crisp. O’Neill had some well-fancied rides in the race, including the ill-fated favourites, Rag Trade and Alverton, in 1978 and 1979, respectively, although he later admitted, “Never at any stage did I think I was going to win any of them.”
O’Neill retired as a jockey in 1986, but even joining the training ranks did little, or nothing, to improve his fortune in the Grand National. In 2004, Clan Royal was only headed in the final hundred yards after jockey Liam Cooper lost his whip at the fourth last fence, eventually finishing second, beaten 3 lengths, behind Amberleigh House. In 2005, despite a broken breast girth and slipping saddle, the same horse, ridden by A.P. McCoy, was 6 lengths ahead and travelling ominously well when carried out by a loose horse at Becher’s Brook on the second circuit; Simply Gifted, ridden by Brian Harding, finished third, at 66/1, in the same race.
In total, O’Neill saddled 14 runners in the National without success but, in 2010, his luck changed. Don’t Push It, again ridden by A.P. McCoy was backed into 10/1 joint favourite and, having led over the last, forged clear in the closing stages to beat Black Apalachi by 5 lengths. O’Neill later reflected on the victory, saying, “I think we’ll always remember the magical day he won the Grand National as it was one of the greatest afternoons in the life of myself, [owner] J.P. [McManus] and A.P. as we had all been trying to win the race for so many years”.