A native of London, England, Byrne left home at 15 to begin a riding career. His journey took him through England, France, Ireland and Belguim and seven years later to the U.S. in 1978. He worked for trainer John Russell at the Phipps family stable in New York, exercised horses and rode some jumpers. Byrne worked for Tony Doyle, LeRoy Jolley, and David Whitely and was an assistant to Howie Tesher. While working for Tesher, he met his wife-to-be, Jill, the daughter of trainer Peter Howe. Jill Byrne is a handicapper and simulcast television personality at Churchill Downs. Byrne went out on his own in 1986. He gained national prominence in 1997 with the 2-year-olds Favorite Trick and Countess Diana, whose Breeders' Cup wins carried them to Eclipse Awards. Favorite Trick became the first 2-year-old since Secretariat to be voted Horse of the Year. Byrne gave up his public stable to be a private trainer for Frank Stronach and orchestrated Awesome Again's perfect six-race 1998 season that culminated with a victory in the Breeders' Cup Classic. Stronach and Byrne parted ways in 1999 and Byrne re-opened his public stable based in Louisville.