Roaring Lion was a grey colt bred in Kentucky by RanJan Racing Inc. As a yearling he was offered for sale at Keeneland in September 2016 and bought for $160,000 by the bloodstock agent David Redvers.

[4] Roaring Lion made his debut in a minor race over one mile at Newmarket's July Course on 18 August in which he was ridden by Harry Bentley and started at odds of 7/2 in a ten-runner field.

[5] Three weeks later, on the synthetic polytrack surface at Kempton Park Racecourse, the colt started 4/5 favourite for a similar event despite carrying a six pound weight penalty.

[9] Roaring Lion began his second season by starting odds-on favourite for the Craven Stakes (a major trial race for the 2000 Guineas) over the Rowley Mile on 19 April.

In the 2000 Guineas over the same course and distance sixteen days later he started a 14/1 outsider and came home fifth behind Saxon Warrior, Tip Two Win, Masar and Elarqam, beaten two and a half lengths by the winner.

[11] On 3 June 2018 Roaring Lion was one of twelve colts to contest the 239th running of the Derby Stakes over one and a half miles at Epsom Racecourse and started the 6/1 second favourite behind Saxon Warrior.

After racing towards the rear and turning into the straight in ninth place he moved up to challenge the leaders approaching the final furlong and finished third behind Masar and Dee Ex Bee.

[12] The Eclipse Stakes over ten furlongs at Sandown Park Racecourse on 7 July saw Roaring Lion matched against older horses in a seven-runner field which included Saxon Warrior, Happily, Hawkbill and Cliffs of Moher.

"[16] The Irish Champion Stakes over ten furlongs at Leopardstown Racecourse on 15 September saw Roaring Lion start the 8/11 favourite ahead of his old rival Saxon Warrior in their sixth meeting.

He started the 2/1 favourite ahead of Recoletos (Prix du Moulin) and Laurens while the other ten runners included Addeybb, Lord Glitters, Lightning Spear and Romanised.

Racing on soft ground he settled in mid-division as Hay Gaman set the pace Roaring Lion began to make progress down the centre of the track in the last quarter mile, he gained the advantage from the outsider Century Dream inside the final furlong and held off the challenge of the Irish filly I Can Fly to win by a neck.

[21] For his final race, Roaring Lion was sent to the United States to contest the Breeders' Cup Classic on dirt at Churchill Downs on 3 November and started the 8/1 fifth choice in the betting.

[25] In early August, shortly after leaving quarantine, Roaring Lion became seriously ill with horse colic and underwent surgery twice to remove sections of his small intestine.