Costello won his first Grade race in November 2006, when he rode Crow Wood to victory in the Grade 2
Elite Hurdle at
Wincanton for Quinn. He won the same race the following year on Kings Quay, also trained by Quinn. He achieved his first Grade 1 success when Wayward Prince, trained by Ian Williams, won the
Sefton Novices' Hurdle at
Aintree in April 2010. Later that year, there was another notable Aintree victory, when
Monet's Garden won the
Old Roan Chase for trainer
Nicky Richards. The following month he had his first ride in the
Grand National, on Postmaster, trained by Tim Vaughn, who was pulled up at the 22nd fence. He also rode in the Grand National in 2013, coming ninth on Saint Are, and in 2015, coming nineteenth on Dolatulo. In 2016 he rode as stable jockey to
Middleham trainer Karl Burke, whose filly Quiet Reflection provided him with success in the
Prix Sigy in April 2016, the
Sandy Lane Stakes the following month, the Group 1
Commonwealth Cup at Royal Ascot and the Group 1
Haydock Sprint Cup in September. Since making the switch in codes, Costello still rides occasionally over jumps. ==Personal life==