[3] He achieved his first Cheltenham Festival win in March 2017, when he rode Champagne Classic, trained by Gordon Elliott, to victory in the Martin Pipe Conditional Jockeys' Handicap Hurdle.
[3] In February 2018, he won his first Grade 1 race on Tower Bridge in the Golden Cygnet Novice Hurdle at Leopardstown for his cousin Joseph Patrick O'Brien.
[5] A second win in the race for Slevin came six years later on the grey Intense Raffles, trained by Thomas Gibney and owned by Simon Munir and Isaac Souede.
[4] Following the retirement of Daryl Jacob on 29 December 2024, Slevin was offered the role of retained jockey in Great Britain and Ireland for owners Munir and Souede.
On his first day in his new role, 2 January 2025, he partnered Al Kalila and O'Toole to win at Ayr in the double green colours of Munir and Souede.