[6] Bradley propelled Findlay College Prep to the National High School Basketball championship game against Oak Hill Academy, winning the contest 56–53.

After leading Findlay to the title, Bradley was named National High School Basketball Player of the Year by Parade Magazine.

Bradley and University of Washington recruit Abdul Gaddy led Bellarmine Prep to the Class 4A State Semifinals with a 25–4 mark as a junior.

[13] On January 14, 2011, Bradley was assigned to the Maine Red Claws of the NBA Development League and on the same day made his debut game for the team, playing 21 minutes and scoring 11 points.

[18] With Bradley still sidelined for the beginning of the 2012–13 NBA season, the aging Celtics struggled with the duo of Courtney Lee and Jason Terry receiving the majority of minutes at shooting guard.

The Celtics lost any realistic chance of contention after point guard Rajon Rondo went down with a torn ACL on January 27,[20] leaving them without their most dynamic player.

Bradley, whose play in the series had mirrored the ineffectiveness of the team, provided a gutsy effort at the end of the game, making all four of his shots and stealing the ball three times in the last ten minutes.

The Celtics ended an era on the day of the 2013 NBA draft, trading aging stars Kevin Garnett and Paul Pierce, as well as Jason Terry and D. J.

[21] However, new Celtics coach Brad Stevens professed his trust in Bradley, who, in the absence of the injured Rondo, began the 2013–14 NBA season as the team's starting point guard.

The move worked brilliantly, as the Celtics immediately went on a four-game winning streak and the more comfortable Bradley settled nicely into his role on the team.

[23] Although the Celtics' lack of talent and experience began to show itself as the season went along, particularly with Rondo still out, Bradley was a rare bright spot, increasing his scoring average every month through January.

[22] He shouldered a higher percentage of the offensive workload for Celtics in 2013–14, and Bradley responded by greatly improving his shooting from the previous season.

Bradley continued to play harassing defense and scored in double digits in 13 of the team's first 15 games,[34] including a career-high 32 points in a loss to the Dallas Mavericks.

Meanwhile, Bradley's offense cooled off in December, as he shot just 39 percent from the field for that month and made just 1-of-21 three-point attempts over a six-game stretch.

Faced with a 9–14 record on December 18, Celtics President of Basketball Operations Danny Ainge made the difficult decision to part with Rondo, trading him and rookie Dwight Powell to the Dallas Mavericks for Brandan Wright, Jae Crowder, Jameer Nelson and two draft picks.

[36] Pundits such as Bill Simmons and Jalen Rose portrayed the trade as a surrender to a mediocrity, with the hopes of getting a high draft pick at season's end,[37] and the Celtics continued to struggle after Rondo's exit.

After failing to post winning records in November, December or January, they did so in February, March, and April, and won eight of the season's last nine games.

Acquiring veteran forwards David Lee and Amir Johnson to fortify their frontcourt, the team also hoped to see the continued improvement of their promising young players, including Marcus Smart and Jared Sullinger.

Bradley provided a rare highlight, however, throwing down a tremendous dunk on reigning Defensive Player of the Year Kawhi Leonard.

Bradley missed three games in early January with a hip injury,[46] and upon his return, the Celtics emerged as one of the top teams in the Eastern Conference.

[47] Eight days later, Bradley connected on a game-winning three-pointer to give Boston a narrow 104–103 victory over the Eastern Conference-leading Cleveland Cavaliers.

[48][49] On February 29, he blocked a shot from Utah Jazz forward Gordon Hayward with 23 seconds left in the game to give the Celtics a victory.

Drawing the Atlanta Hawks in the first round of the playoffs, the Celtics narrowly lost in Game 1, as Bradley scored 18 points but went down in the fourth quarter with an apparent right hamstring injury.

Beginning with an opening night 17-point performance that included 3-of-4 three-point shooting, Bradley enjoyed his most effective offensive season, although injuries limited him to just 55 games.

Bradley managed double digit rebounds on 10 occasions, including November 16, when he recorded a career-high 13, to go along with 18 points, in a victory over the Dallas Mavericks.

On July 7, 2017, in a bid to clear enough cap space to sign star free agent Gordon Hayward, as well as an attempt to increase the size of their perimeter defenders,[63] the Celtics traded Bradley and a 2019 second-round draft pick to the Detroit Pistons in exchange for Marcus Morris.

The season resumed, but Bradley opted out of playing in the restart to remain with his family due to his oldest child, six-year-old son Liam, who had a history of struggling to recover from respiratory illnesses.

[80] On March 25, 2021, Bradley, Kelly Olynyk, and a 2022 draft pick swap were traded to the Houston Rockets in exchange for Victor Oladipo.

However, he rarely displayed his elite leaping ability in games, occasionally blocking players at the rim or throwing down dunks but more often simply harassing his man on the perimeter and settling for layups.

Bradley's intense and frenetic defensive style of play, probably his most valuable asset, may also be partly to blame for the series of injuries he has suffered in his career.