In the Horizon league tournament, Stevens’ Bulldogs used their home-court advantage to beat Milwaukee 68–59 in the semi-finals and to beat Wright State 70–45 in the finals. The win earned the team an automatic bid into the 2010 NCAA tournament, and completed a 20–0 run through league play. Stevens became the first coach to lead a Horizon League team to both an undefeated regular season and conference tournament since the league was formed in 1979. Stevens was also the only coach in Division I to lead his team to an undefeated conference schedule during the 2009–10 season.

Stevens attended Zionsville Community High School, where he became a star basketball player. He wore No. 31 in high school in honor of Indiana Pacers guard Reggie Miller. During his freshman year, he got up early to practice shooting at a local gym before school. The hard work paid off as Stevens made the varsity team that year. By the time his high school career was complete, Stevens had set school records for career scoring, assists, steals, and three-point field goals. As of 2017, he still holds the records for career points per game average (26.8), total career points (1508), assists (444), and steals (156), as well as the single-season points record (644 in 1995). Stevens was named to the all-conference team three times. In 1995, he was the sectional MVP and the leading scorer in state sectional play (32.3 ppg).

Stevens is known for projecting a professional, “corporate” look from the sidelines. Asked what his life would be like if he had never taken up coaching, he replies “If everything else remained the same, I would have been as happy as heck… Friends and family and faith, they’re going to take the cake over all this stuff.” Stevens met his wife, Tracy (née Wilhelmy), while attending DePauw University. Tracy, who played soccer for DePauw, quickly learned of Brad’s love for basketball; on their third date he drove her an hour and a half to attend a high school basketball game. Tracy graduated from Rocky River High School in 1995, and from DePauw in 1999. She returned to school in 2000, driving five hours from Case Western’s law school to Indianapolis on weekends to see Stevens. She finished her final year of law school in Indianapolis, and the couple married in August 2003. Tracy works as a labor and employment lawyer, and also serves as Stevens’ agent.

At DePauw, Stevens was a member of the Management Fellows Honors Program and the DePauw Community Services’ Sports Night executive board. He was also a brother of the Alpha Tau Omega fraternity. During summer vacations, Stevens spent time teaching at Butler basketball camps. He was named to the Dean’s list and graduated in 1999 with a degree in economics.

Stevens rallied the team, and they proceeded to win 16 straight games before facing Siena in a BracketBusters game. Butler beat Siena 70–53 and Stevens tied the NCAA record for most wins (81) by a head coach in his first three seasons set by Mark Few of Gonzaga in 2002 and tied by Mark Fox of Nevada in 2007.

Brad and Tracy are involved with the American Cancer Society’s Coaches Vs. Cancer. He says that the cause really hit home for them after Tracy’s mother died of the disease in June 2004. The day before Butler’s 2010 Final Four appearance, they hosted a fundraiser for the organization. Stevens has also volunteered his time to the Jukes Foundation for Kids, a charity benefiting Ugandan children run by former Butler player Avery Jukes. Stevens remains in close contact with the Butler basketball family; he notably took a one-game leave from the Celtics in January 2016 to visit with Andrew Smith, a player on both of Butler’s Final Four teams who was dying of cancer; Smith died less than a week later. At the request of Andrew’s widow, Sam, Stevens delivered the eulogy at the memorial service on January 17, 2016.

On April 2, 2007, Lickliter resigned in order to take the head-coaching position at the University of Iowa. The Butler players had a meeting with athletic director Barry Collier, urging him to promote from within. Collier, having spent the entire season observing the assistant coaches’ interaction with the team, agreed. The day after Lickliter resigned Stevens and Butler’s two other assistant coaches interviewed for the job. Within 24 hours of the interviews Stevens was named Butler’s new head coach. According to Collier, Stevens had something older, outside candidates could never match: six years of experience learning the Butler system, dubbed “The Butler Way” by Collier. “Age wasn’t a factor because I’d seen his ability shine through during the course of the season,” Collier said.

On February 26, 2010, Butler traveled to Valparaiso for their regular season finale. Leading scorer Gordon Hayward was sidelined with lower back pain, but the team still won 74–69. In so doing, Stevens broke the coaching record he had tied the prior week and Butler completed an 18–0 undefeated conference schedule. It was Butler’s first undefeated conference record since joining the Horizon League, and first since Joe Sexson led the 1978 team to a 6–0 record in the now defunct Indiana Collegiate Conference. Stevens earned his third straight regular-season conference championship.

On March 25, 2010, Butler faced top-seeded Syracuse. The Bulldogs got off to a good start, jumping out to a 12–1 lead and a 35–25 halftime advantage. Syracuse rallied in the second half, taking its first lead of the game, 40–39, off a Wes Johnson three-pointer. Stevens called timeout and Butler regained the lead on its next possession, stopping the run. At the 5:32 mark, Syracuse got a rare fast break opportunity that ended with a dunk and 54–50 lead. Stevens again called time out and re-focused the team. Butler responded by holding Syracuse scoreless for the next 5 minutes, taking a 60–54 lead with 0:59 to go. Butler held on to win 63–59, advancing to the Elite Eight for the first time in school history.

On April 5, 2010, Butler and Duke faced off in what The New York Times called “the most eagerly awaited championship game in years”. Late in the first half, Duke went on an 8–0 run to take a 26–20 lead. Stevens called a timeout. With starters Matt Howard and Ronald Nored on the bench in foul trouble, Stevens was forced to call on backup center Avery Jukes who came up big for Butler. Jukes scored 10 first half points, tying his season high. At half time, Duke’s lead stood at 33–32.

On April 8, 2010, Stevens signed a long-term deal with Butler, extending his contract through the 2021–22 season. Financial terms of the contract were not disclosed; however, Butler president Bobby Fong had publicly stated that the university could afford to increase Stevens’ base salary to approximately US $1,000,000 a few days prior. Stevens had previously made US$395,000 plus benefits in base salary, a relatively low figure for a successful Division I head basketball coach. His total compensation for 2009–10 was estimated at US$750,000. Stevens had received a raise after each of his three seasons at Butler and his contract contains a buyout clause estimated in the high six or low seven figures.

Stevens is a proponent of statistical analysis to enhance his coaching decisions, spending almost as much time looking at statistics as watching game film. “I think it’s a unique way of looking at the game that may be able to help best communicate to your players”, he explains. For example, when Butler was slumping in late 2010, Stevens challenged his team: “this [46% defensive field goal percentage] is where we are. This isn’t acceptable to get to where we want to go. But what does that really mean? It’s not just get better defensively, it is, if we give up 3 less baskets a game, then we will be at 40 percent field goal percentage defense which will be top 20 in the country”. The team got the message, improved throughout the season, and ultimately went on a March run fueled by defense. In 2012, Stevens became the first college coach to hire someone solely for statistical research when he added Drew Cannon to the staff. If he had the resources, Stevens says he would hire a team of statisticians to analyze the team’s play.

Picked by many to lose a first-round match-up against Old Dominion, Butler advanced on a last-second tip-in by Howard. Howard was also clutch in their next game, hitting a free throw with a less than one second remaining to beat Pitt in a dramatic finish. Shelvin Mack scored 30 points in the win. Butler won their next game when they defeated Wisconsin. On March 26, 2011, the Bulldogs beat Florida 74–71 in overtime to earn back-to-back trips to the Final Four. On April 2, Butler beat fellow Cinderella team VCU 70–62 to make it to a second consecutive national championship game. For the second consecutive year, the Bulldogs fell in the national championship game, this time to Connecticut.

In March 2013, UCLA reportedly offered Stevens between $2.5 and $3 million a year to leave Butler. Rumors circulated that Stevens was in contract negotiations with UCLA, but ultimately the rumors proved false and Stevens stayed at Butler. Commenting on the situation, a source close to Stevens said “Brad doesn’t understand why people would assume he’s leaving.” A few days later, Stevens reiterated that he was very happy at Butler and had no intentions to leave as long as he had the support of the university to continue running the program the “right way”.

On July 3, 2013, Stevens was signed as the head coach for the Boston Celtics to coach in the NBA. In April 2015, in his second season as head coach, Stevens led the Celtics to the 2015 playoffs as the seventh seed in the Eastern Conference with a 40–42 record. On April 21, 2015, it was announced that Stevens finished fourth in voting for the NBA’s Coach of the Year Award. In April 2016, Stevens led the Celtics to their second consecutive playoff appearance as the fifth seed in the 2016 playoffs, finishing the season with a 48–34 record.

On April 16, 2015, Stevens was named the Eastern Conference Coach of the Month for April. He led the Celtics to the East’s best record in April at 7–1. The Celtics recorded a 4–0 mark on the road, and closed the month with six consecutive victories – five of them against playoff teams. On February 28, 2016, Stevens was named the Eastern Conference Coach of the Month for February. He guided his squad to an Eastern Conference-best 9–3 record during the month, including a perfect 6–0 mark at home. The Celtics (36–25 overall) finished the month in sole possession of third place in the East behind the Cleveland Cavaliers and Atlantic Division foe the Toronto Raptors.

On June 1, 2016, Stevens received a contract extension. On February 3, 2017, Stevens was named the Eastern Conference head coach for the 2017 NBA All-Star Game. In April 2017, in his fourth season as head coach, Stevens led the Celtics to the 2017 playoffs as the first seed in the Eastern Conference with a 53–29 record. They reached the Eastern Conference Finals, where they lost to the defending champion Cleveland Cavaliers in five games.

On July 4, 2017, Stevens was reunited with his former college player Gordon Hayward when Hayward signed a contract to play for the Celtics. In the 2017–18 season, the Celtics’ roster saw a massive change, as two-time All-Star Isaiah Thomas was traded to the Cleveland Cavaliers in exchange for Kyrie Irving. Stevens and the Celtics went 55–27, finishing the season as the second seed in the Eastern Conference, despite losing Hayward for the season to a broken ankle in the first game of the season and Irving missing significant playing time due to knee injuries. Despite Irving missing the playoffs, Stevens led the Celtics on a deep playoff run, losing to the Cleveland Cavaliers in seven games in the Eastern Conference Finals. Stevens was considered a front runner for the NBA Coach of the Year Award, but lost to Dwane Casey of the Toronto Raptors.