2005: two-year-old season

Dylan Thomas made his first racecourse appearance in a maiden race at Tipperary on 30 June. Ridden by Kieren Fallon, he started even money favourite and won by a length from Galantas.^[1] He was off the racecourse until 10 September when he ran in the Irish Breeders' Foal Levy Stakes at Leopardstown. He took the lead two furlongs from the finish and won by three quarters of a length from Royal Power despite hanging badly to the right in the closing stages.^[2] Dylan Thomas was then sent to England to contest the Group Three Autumn Stakes at Salisbury on 8 October. Ridden by Johnny Murtagh, he started 13/8 favourite, but after leading briefly in the straight he finished second by a neck to Blitzkrieg. The future Dubai World Cup winner Well Armed finished fourth.^[3] Three weeks later, Dylan Thomas was moved up to Group One class for the Racing Post Trophy at Doncaster. He made little impression and finished sixth of the seven runners behind Palace Episode.

2006: three-year-old season

Dylan Thomas made his three-year-old debut in the Derrinstown Stud Derby Trial over ten furlongs at Leopardstown on 14 May. Ridden by Seamie Heffernan he took the lead early in the straight and stayed on strongly to win from his stable companion Mountain and the English challenger Youmzain.^[4] On 3 June, he lined up for The Derby. Ridden by Johnny Murtagh, he was sent to the lead after half a mile and stayed there until headed on the line by winner Sir Percy and runner-up Dragon Dancer. He subsequently won the Irish Derby at the Curragh, ridden by Kieren Fallon. After a summer break, Dylan Thomas beat Ouija Board in a thrilling finish to the Irish Champion Stakes in September.

In late September 2006, Coolmore took the unusual step of sending Dylan Thomas to run in the Jockey Club Gold Cup at Belmont Park, his first (and only) race on dirt where he raced against top US dirt 3yo Bernardini. He never took to the surface and struggled from the break, trailing in a distant last.

2007: four-year-old season

As a four-year-old in 2007, Dylan Thomas won the Prix Ganay at Longchamp in France, and the King George VI and Queen Elizabeth Stakes at Ascot, the latter under Johnny Murtagh. On 8 September 2007 he became the first two-time winner of the Irish Champion Stakes and rider Kieren Fallon became the first jockey to win the race three times in succession. He crowned this season with a win in the Prix de l'Arc de Triomphe on soft ground. The victory stood after a half-hour stewards enquiry into interference was caused because Dylan Thomas veered sharply to the right halfway up the home straight, thereby coming across two other runners. Prior to this race, Fallon had described Dylan Thomas as the best horse he had ever ridden.

After the Prix de l'Arc de Triomphe, Dylan Thomas was entered in the John Deere Breeders' Cup Turf, but he did not contend. After he was withdrawn from the Japan Cup, his last race was the Hong Kong Vase, in which he finished 7th. Dylan Thomas retired to Coolmore Stud in Ireland before the end of the year. He raced for Michael Tabor and Susan Magnier, whose husband, John Magnier, is Coolmore's managing partner.