In that first part of the 2015/16 National Hunt campaign he recorded his first major successes for his uncle Willie Mullins, initially winning a Grade 2 event on board of Devis Bride.

[2] Shortly after that he obtained his first Grade 1 victory when taking the Morgiana Hurdle in a tactical affair on board of Nichols Canyon, producing the surprise of the season by defeating the champion hurdler Faugheen who was unbeaten at the time.

[3] During the same season he continued to win more Graded races for other trainers such as Ms Sandra Hughes and Pat A. Fahy and culminated with a victory for Mouse Morris in the most valuable race of the Jumps calendar, the 2016 Grand National at only his first attempt, giving a patient ride to Rule The World,[4] a horse which had never previously won a steeplechase.

[5] He became one of the youngest jockeys ever to win the race and declared: →"It's a weird feeling, you don't really believe it" →"I beat Faugheen on Nichols Canyon but I think this tops that".

[8] In November 2024, Mullins purchased the horse Kindly Prince for £320,000 at the Goffs Coral Gold Cup Sale, Newbury.