He commenced racehorse training in 1988  having previously worked as an assistant to his father Paddy Mullins and Jim Bolger. Willie is a former six times amateur champion jockey in Ireland, winning the 1983 Aintree Fox Hunters' Chase on Atha Cliath and the 1996 Cheltenham Bumper on Wither Or Which.
He is the trainer of the 2005 Grand National winner Hedgehunter and the 2011 and 2013 Champion Hurdle winner Hurricane Fly and trained the horse, Vautour in the 2016 Ryanair Chase. He is also trainer of the six times David Nicholson Mares' Hurdle champion, Quevega. In 2015 Willie Mullins became the first trainer to train the top 3 horses in the Champion Hurdle. In the 2015 Cheltenham Festival Willie Mullins trained 8 winners which is a joint record at the Cheltenham Festival that Gordon Elliott equalled in 2018. He is the leading most winning trainer at the Cheltenham festival and was awarded in their prestigious hall of fame.
Mullins' long lasting relationship with Gigginstown House Stud came to an end on 28 September 2016. Despite this he was the Irish Champion trainer in the 2016/17 season.
Willie Mullins has a son, Patrick Mullins, who is currently an amateur jockey riding mainly in Ireland for his father. Patrick is also an assistant trainer to his father. Willie's wife, Jackie, was a successful amateur rider.
- Clower, Michael (2007). Kings of the Turf. London: Arum Press Ltd. p. 39. ISBN 1845132793.
- "Willie Mullins". BBC Sport. 8 April 2005. Retrieved 17 March 2018.
- Willie Mullins at Horse Racing Ireland
- "Cheltenham Festival winners". WP Mullins. Retrieved 17 March 2018.
- "Cheltenham Festival: Punjabi So Brave For Henderson" dailyrecord.co.uk, 11 March 2009, accessed 11 March 2009
- "Willie Mullins Champion Hurdle 1-2-3". Daily Mail. Retrieved 14 March 2015.
- "Trainer Willie Mullins scoops eighth win to break festival record". Irish Mirror. Retrieved 14 March 2015.
- Peacock, Tom (16 March 2018). "Cheltenham 2018: Final triumph crowns 'golden era' in Irish racing". The Irish Times. Retrieved 17 March 2018.
- "Willie Mullins and Gigginstown House in split, Gordon Elliott to train Don Poli". At The Races. Retrieved 5 March 2018.
- Mullins clan immersed in the business of racing, Irish Times, March 11, 2016.
- Willie Mullins' Official Website
- Willie Mullins' Cheltenham Festival Winners
- Willie Mullins' Horses in training
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