On May 20, 2015 at NXT TakeOver: Unstoppable, Joe made his debut during the main event as a face, stopping Kevin Owens from attacking an injured Sami Zayn with a chair and having a stare-down with Owens.
While initially Joe was allowed to also continue working outside WWE, on June 1, it was reported that WWE had decided to sign him to a full-time deal due to his impressive merchandise sales.
Joe made his in-ring debut on the June 10 episode of NXT, defeating Scott Dawson.
On the June 17 episode of NXT, a match between Joe and Owens ended in a no contest, with the two continuing to brawl after the match until they were separated.
At NXT TakeOver: Brooklyn, Joe defeated Baron Corbin by technical submission.
Joe was then paired with NXT Champion Finn Bálor to enter the Dusty Rhodes Tag Team Classic tournament, which they won after defeating The Lucha Dragons (Kalisto and Sin Cara) in the first round, Enzo Amore and Colin Cassady in the quarter-finals, The Mechanics (Dash Wilder and Scott Dawson) in the semifinals and Baron Corbin and Rhyno in the finals at NXT TakeOver: Respect.

On the November 4 episode of NXT, Joe turned heel by attacking Finn Bálor after Bálor's match against Apollo Crews.
On the November 11 episode of NXT, it was explained that Joe was not granted a NXT Championship match against Bálor despite his verbal commitment.
On December 16 at NXT Takeover: London, Joe was unsuccessful in his title match against Bálor.
On the January 13, 2016 episode of NXT, Joe challenged Corbin and the returning Sami Zayn to a number one contender's match.
The match took place on the January 27 episode of NXT, but ended in a no contest when Corbin submitted to both opponents at the same time.
Joe and Zayn then had a #1 contender rematch on the February 17 episode of NXT, which ended in a draw.
This led to a two out of three falls match on the March 9 episode of NXT, which Joe won the match two falls to one to earn another NXT Championship match against Bálor at NXT TakeOver: Dallas on April 1, which he lost after suffering a large laceration to his right cheek minutes into the match.

On April 21 at a NXT live event, Joe defeated Bálor to win the NXT Championship.
In his first title defense, Joe defeated Bálor in a steel cage match on June 8 at NXT TakeOver: The End.
Joe then engaged in a feud with Shinsuke Nakamura, who defeated him in a title match on August 20 at NXT TakeOver: Brooklyn II, ending his reign of 121 days.
During the match, Joe suffered a legitimate dislocated jaw.
On November 19 at NXT TakeOver: Toronto, Joe defeated Nakamura in a rematch to win back the title and became the first ever two-time NXT Champion.
However, he lost the title back to Nakamura on December 3, 2016 in Osaka, Japan, ending his reign at 14 days and the shortest in the title's history.
On December 8, 2016, in Melbourne, Australia, Joe and Nakamura's feud would come to an end with Nakamura successfully defending his NXT Championship against Joe in a steel cage match.
On the January 25, 2017, episode of NXT, Joe would team with Bobby Roode in an unsuccessful effort against Nakamura and Tajiri.
Joe would appear in the crowd at NXT TakeOver: San Antonio.
On May 20, 2015 at NXT TakeOver: Unstoppable, Joe made his debut during the main event as a face, stopping Kevin Owens from attacking an injured Sami Zayn with a chair and having a stare-down with Owens. While initially Joe was allowed to also continue working outside WWE, on June 1, it was reported that WWE had decided to sign him to a full-time deal due to his impressive merchandise sales. Joe made his in-ring debut on the June 10 episode of NXT, defeating Scott Dawson. On the June 17 episode of NXT, a match between Joe and Owens ended in a no contest, with the two continuing to brawl after the match until they were separated. At NXT TakeOver: Brooklyn, Joe defeated Baron Corbin by technical submission. Joe was then paired with NXT Champion Finn Bálor to enter the Dusty Rhodes Tag Team Classic tournament, which they won after defeating The Lucha Dragons (Kalisto and Sin Cara) in the first round, Enzo Amore and Colin Cassady in the quarter-finals, The Mechanics (Dash Wilder and Scott Dawson) in the semifinals and Baron Corbin and Rhyno in the finals at NXT TakeOver: Respect. 
On the November 4 episode of NXT, Joe turned heel by attacking Finn Bálor after Bálor's match against Apollo Crews. On the November 11 episode of NXT, it was explained that Joe was not granted a NXT Championship match against Bálor despite his verbal commitment. On December 16 at NXT Takeover: London, Joe was unsuccessful in his title match against Bálor. On the January 13, 2016 episode of NXT, Joe challenged Corbin and the returning Sami Zayn to a number one contender's match. The match took place on the January 27 episode of NXT, but ended in a no contest when Corbin submitted to both opponents at the same time. Joe and Zayn then had a #1 contender rematch on the February 17 episode of NXT, which ended in a draw. This led to a two out of three falls match on the March 9 episode of NXT, which Joe won the match two falls to one to earn another NXT Championship match against Bálor at NXT TakeOver: Dallas on April 1, which he lost after suffering a large laceration to his right cheek minutes into the match.
On April 21 at a NXT live event, Joe defeated Bálor to win the NXT Championship. In his first title defense, Joe defeated Bálor in a steel cage match on June 8 at NXT TakeOver: The End. Joe then engaged in a feud with Shinsuke Nakamura, who defeated him in a title match on August 20 at NXT TakeOver: Brooklyn II, ending his reign of 121 days. During the match, Joe suffered a legitimate dislocated jaw. On November 19 at NXT TakeOver: Toronto, Joe defeated Nakamura in a rematch to win back the title and became the first ever two-time NXT Champion. However, he lost the title back to Nakamura on December 3, 2016 in Osaka, Japan, ending his reign at 14 days and the shortest in the title's history. On December 8, 2016, in Melbourne, Australia, Joe and Nakamura's feud would come to an end with Nakamura successfully defending his NXT Championship against Joe in a steel cage match. On the January 25, 2017, episode of NXT, Joe would team with Bobby Roode in an unsuccessful effort against Nakamura and Tajiri. Joe would appear in the crowd at NXT TakeOver: San Antonio.
Samoa Joe