Since joining NJPW in 2016, the young high flyer has made a huge splash on the Juniors scene. Debuting in the UK in 2012, he earned many titles and accolades in the local circuit. In April of 2016, he joined NJPW at the behest of Kazuchika Okada, who was impressed by the “Aerial Assassin’s” technique. At the age of 23 he became the youngest winner of the Best of the Super Juniors tournament.

Ospreay would quickly become a focal point of the Junior Heavyweight Division, with regular match of the year candidate performances and intense rivalries against KUSHIDA, Hiromu Takahashi, and longtime nemesis, countryman Marty Scurll.  At the same time, Ospreay was determine to not lose out to the heavyweight contenders, and was always open to pit himself against the top stars of the higher weight classes. At NJPW’s 46th Anniversary Event, then IWGP Junior Heavyweight Champion Ospreay took on then IWGP Heavyweight Champion Kazuchika Okada in a special exhibition match that held audiences around the world in rapture. 

Ospreay lost the Junior Heavyweight Championship to Hiromu Takahashi at Dominion 2018, but was buoyed by his performance against Okada to move on. Gaining weight, and adjusting his style to be more adaptable to a range of opponents, he set his sights on the NEVER Openweight Championship, a title he won by beating idol Kota Ibushi at Wrestle Kingdom 13. A stronger, meaner Ospreay, the new champion vowed to make his a truly openweight championship, one he wanted to defend against both juniors and heavyweights. In 2019’s New Japan Cup, he proved himself against much larger opponents Bad Luck Fale and Lance Archer, before taking on athletic powerhouse Jeff Cobb at G1 Supercard in a double title match with both NEVER and ROH TV Championships up for grabs. 

Ospreay came up short in MSG, but would go onto the biggest summer of his career. In June, he would win Best of the Super Juniors, handing Shingo Takagi his first NJPW pinfall loss in the process. The very same week, he would defeat Dragon Lee to win his third IWGP Junior Heavyweight Championship. He went on to enter the G1 Climax, becoming the very first to be part of the New Japan Cup, Best of the Super Juniors and the G1 in the same calendar year. He finished with a record of 4 wins and 5 losses.

On January 4 2020, Ospreay was unsuccessful in his defence of IWGP Jr. Heavyweight Championship from Hiromu Takahashi, but would direct his attentions to British Heavyweight Champion Zack Sabre Junior. On February 14 at a RevPro event in London, Ospreay pinned ZSJ to become the champion on his fifth attempt, and declared that he would be moving to the heavyweight division permanently going forward.