On December 18, 2014, Crowder was traded, along with Jameer Nelson, Brandan Wright, a 2015 first-round pick, a 2016 second-round pick and a $12.9 million trade exception, to the Boston Celtics in exchange for Rajon Rondo and Dwight Powell.
On January 12, 2015, he scored a then career-high 22 points in a 108–100 win over the New Orleans Pelicans.
On April 14, 2015, he hit an off-balance fall-away two-point shot from deep on the right wing with 0.8 seconds left, lifting Boston to a 95–93 win over the Toronto Raptors.
After averaging just 3.6 points in 10.6 minutes per game with Dallas to start the 2014–15 season, Crowder became an important role player for the Celtics in Brad Stevens' rotation, and subsequently lifted his averages to 9.5 points in 24.2 minutes per game.

On July 27, 2015, Crowder re-signed with the Celtics to a reported five-year, $35 million contract.
On December 18, 2015, he scored a career-high 24 points in a loss to the Atlanta Hawks.
He topped that mark on January 4, 2016, scoring 25 points in a 103–94 win over the Brooklyn Nets.
On January 13, he tied his career high of 25 points in a 103–94 win over the Indiana Pacers.
On March 14, he was ruled out for two weeks with a right ankle sprain.
He returned to action on March 31 against the Portland Trail Blazers after missing eight games.

In the Celtics' season opener on October 26, 2016, Crowder scored 21 points in a 122–117 win over the Brooklyn Nets.
He appeared in the team's first four games of the season, but then missed eight straight games with a sprained left ankle.
He returned to action on November 19, scoring nine points in a 94–92 win over the Detroit Pistons.
On March 17, 2017, he recorded season highs with 24 points and 12 rebounds in a 98–95 win over Brooklyn.
On March 26, 2017, he set a new season high with 25 points in a 112–108 win over the Miami Heat.
In Game 1 of the Celtics' Eastern Conference semifinal match-up with the Washington Wizards, Crowder scored a playoff career-high 24 points, helping the Celtics win 123–111.
On December 18, 2014, Crowder was traded, along with Jameer Nelson, Brandan Wright, a 2015 first-round pick, a 2016 second-round pick and a $12.9 million trade exception, to the Boston Celtics in exchange for Rajon Rondo and Dwight Powell. On January 12, 2015, he scored a then career-high 22 points in a 108–100 win over the New Orleans Pelicans. On April 14, 2015, he hit an off-balance fall-away two-point shot from deep on the right wing with 0.8 seconds left, lifting Boston to a 95–93 win over the Toronto Raptors. After averaging just 3.6 points in 10.6 minutes per game with Dallas to start the 2014–15 season, Crowder became an important role player for the Celtics in Brad Stevens' rotation, and subsequently lifted his averages to 9.5 points in 24.2 minutes per game.
On July 27, 2015, Crowder re-signed with the Celtics to a reported five-year, $35 million contract. On December 18, 2015, he scored a career-high 24 points in a loss to the Atlanta Hawks. He topped that mark on January 4, 2016, scoring 25 points in a 103–94 win over the Brooklyn Nets. On January 13, he tied his career high of 25 points in a 103–94 win over the Indiana Pacers. On March 14, he was ruled out for two weeks with a right ankle sprain. He returned to action on March 31 against the Portland Trail Blazers after missing eight games.
In the Celtics' season opener on October 26, 2016, Crowder scored 21 points in a 122–117 win over the Brooklyn Nets. He appeared in the team's first four games of the season, but then missed eight straight games with a sprained left ankle. He returned to action on November 19, scoring nine points in a 94–92 win over the Detroit Pistons. On March 17, 2017, he recorded season highs with 24 points and 12 rebounds in a 98–95 win over Brooklyn. On March 26, 2017, he set a new season high with 25 points in a 112–108 win over the Miami Heat. In Game 1 of the Celtics' Eastern Conference semifinal match-up with the Washington Wizards, Crowder scored a playoff career-high 24 points, helping the Celtics win 123–111.
Jae Crowder