Will Ospreay made his NJPW debut in 2016 by challenging Kushida for the IWGP Junior Heavyweight Championship but was defeated. Two months later he won the Best of the Super Juniors and therefore has the opportunity to challenge Kushida again, being defeated again.

Later in the year he entered the Super J Cup being eliminated by Matt Sydal in the second round and challenged Katsuyori Shibata for the British Heavyweight Championship being defeated. In 2017 he participates in the Best of The Super Juniors being defeated in the final by Kushida.

In October 2017, Ospreay defeated Kushida to become the IWGP Junior Heavyweight Champion for the first time. He lost the title to Marty Scurll in his first defense, only to regain it at Wrestle Kingdom 12. He lost the title to Hiromu Takahashi in June 2018. At Wrestle Kingdom 13 he defeated Kota Ibushi to become NEVER Openweight Champion, but lost it to Jeff Cobb at G1 Supercard.

He wins the Best of the super juniors for the second time and then the Junior title for the third time at Dominion. He participates in the New Japan Cup and the G1 Climax heavyweight tournaments.