He Knows No Fear, a 300-1 shot at Leopardstown, clinched victory on Thursday to become the longest-priced winner in racing history.
The three-year-old colt was making just his second start and had come 12th of 14 in Limerick in July at a price of 250-1.
Those odds were lengthened this week, but the horse – owned and trained by Luke Comer, and ridden by jockey Chris Hayes – stunned the bookmakers at the Irish Stallion Farms EBF Maiden, beating Agitare by a head.
The record-breaking achievement surpasses Equinoctial's 1990 triumph at Kelso from a starting price of 250-1.
Killahara Castle previously held the Irish record at 200-1 at Thurles in 2017.