Nationality: Ireland

Background:
Age: 27. Donnacha O'Brien is the son of multiple champion trainer Aidan O'Brien and younger brother of former jockey and now trainer Joseph O'Brien. Donnacha is a former jockey, gaining his first Group 1 victory when riding Intricately to win the 2016 Moyglare Stud Stakes. He was Irish flat racing Champion Apprentice Jockey in 2016 and Irish Champion Jockey for the first time in 2018. He retained his riding title in 2019 before opting to train. He has enjoyed plenty of success as a trainer with Porta Fortuna, a prolific Group 1 winner, whiles his latest Group 1 victor was Balantina, who claimed the 2025 Breeders' Cup Juvenile Fillies Turf. As a jockey, O'Brien rode the likes of Magna Grecia, Saxon Warrior and Latrobe to Group 1 wins.

Achievements:
Irish Champion Apprentice Jockey (2016), Irish Champion Jockey (2018 & 2019).

Notable Race Wins Include
Breeders' Cup Juvenile Fillies Turf (2025 Balantina), Cheveley Park Stakes (2023 Porta Fortuna), Coronation Stakes (2024 Porta Fortuna), Criterium International (2022 Proud And Regal), Matron Stakes (2024 Porta Fortuna), Moyglare Stud Stakes (2020 Shale), Nassau Stakes (2020 Fancy Blue), Prix de Diane (2020 Fancy Blue).

Hong Kong Career Wins
(as of 8 April): 0