Brad Miller returned to his home state to attend Purdue University, located in West Lafayette, Indiana, where he played under head coach Gene Keady and assistant coaches Bruce Weber and Frank Kendrick. During his freshman season, along with senior Cuonzo Martin, he led the Boilermakers to a 25–7 record. Along the way, he was part of a Big Ten Conference Title and an NCAA Second Round appearance. He averaged 6.5 points and 5.4 rebounds a game.
During his sophomore season, he helped lead Purdue, along with fellow sophomore Chad Austin, to a three-peat conference title and a consecutive NCAA Second Round appearance. The Boilers finished the season with a 26–6 overall record. Miller averaged 9.6 points and 5.5 rebounds on the season.
His junior season showed more progress than the prior season, averaging 14.3 points and 8.3 rebounds a game. Finishing second in the conference, Miller, along with teammate and former NBA player Brian Cardinal, helped the Boilers to a third straight NCAA Second Round finish. They beat Rhode Island in overtime, where Brad scored 31 points, grabbed eight rebounds and set a school tournament record with made/attempted free throws, going 15–21 from the line. He finished his junior season with an 18–12 record. Throughout his junior year, Miller became the only center in Purdue history to lead the team in assists.
Brad Miller had his best college season during his senior year, helping with a 28–8 record. Averaging 17.2 points and 8.8 rebounds in his last season at Purdue, he led the Boilermakers to a Sweet Sixteen appearance and a 2nd overall seed in the NCAA Tournament. Miller set a school tournament record with 6 steals in a win against Delaware. His last collegiate game was a loss to Stanford. Near the end of the game, Brad busted his chin multiple times and kept going out on the floor. Miller's biggest game of his senior season came against Michigan State, where he scored 30 points and pulled down 12 rebounds to force Michigan State to share their Big Ten crown.
During his career at Purdue, he became one of only five players (Joe Barry Carroll, Terry Dischinger, Walter Jordan and Robbie Hummel) to record 800 rebounds and the first player in school history to have 1,500 points, 800 rebounds and 250 assists. Robbie Hummel has since exceeded Millers totals: (1,772 points, 862 rebounds and 262 assists).
After college, because of the NBA lockout, Miller started his career in the Italian Serie A with Bini Viaggi Livorno for three months. He was then signed by the Charlotte Hornets as an undrafted free agent. He played for the Hornets for two seasons. On March 24, 1999, he had 25 points, going 9–9 shooting and 7–7 from the line. On May 5, 1999 scored a season high 32 points to go along with 13 rebounds in a win against the Boston Celtics. The Hornets made it to the playoffs the following season where they lost 1–3 to the Philadelphia 76ers. In his first playoff series, Miller averaged 7,5 points on 52 percent shooting.
After two seasons with the Hornets, he signed with the Chicago Bulls as a free agent. In January 2002, he was involved in an on-court altercation with center Shaquille O'Neal of the Los Angeles Lakers. After he and Charles Oakley gave a hard foul on O'Neal, Miller walked away as O'Neal swung at the back of his head. Nearly doubling his playing time with the Bulls, he averaged 12.7 points a game, shooting 46 percent during the 2001–02 season.
In February 2002, he was traded by the Bulls with Ron Mercer, Ron Artest (now Metta World Peace) and Kevin Ollie to the Indiana Pacers for Jalen Rose, Travis Best, Norman Richardson, and a second-round draft pick. He wrapped up the 2001–02 season with a 15.1 points and 8.2 rebounds per game average. During his first and only complete season with the Pacers, he made his first NBA All-Star Team becoming one of the first undrafted players to be named an All-Star along with the Detroit Piston's Ben Wallace in the same year. The Pacers clinched a play-off berh for the 6th season in a row, where they lost to the Celtics 2–4.
During the 2003 offseason, Brad was involved in a sign-and-trade with the Sacramento Kings. He was signed to a multi-year deal by Indiana and then traded to the Kings in exchange for Scot Pollard. In the same trade, the Kings sent Hedo Türkoğlu to San Antonio Spurs, San Antonio traded Danny Ferry to Indiana and Indiana traded Ron Mercer to San Antonio. While signing with the Kings, Miller stated, "I wanted to stay with Indiana but my agent said that the money I could make with Sacramento was just too good to pass up and I would never get this kind of contract again." On November 21, 2003 Miller recorded his first career triple-double with 22 points, 14 rebounds, and 10 assists in a win over the Orlando Magic. Less than a month later, Miller recorded another triple-double with 18 points, 15 rebounds and 10 assists. Averaging 14.1 points and 10.3 rebounds in his first season with the Kings, he was voted to back-to-back NBA All-Star Game appearances. Also during that season, Brad scored 1,014 points. In the playoffs, Sacramento lost the Western Conference Semifinals 3–4 to the Minnesota Timberwolves.
Miller appeared in only 56 games during his second season at Sacramento, yet averaging his career high of 15.6 points a game. On February 2, 2005 Miller scored a career-high 38 points to go along with 17 rebounds in a win over the Golden State Warriors. Two days later scored his first back-to-back 30 points game with 35 against the New York Knicks. In the playoffs, Miller averaged a career-high 11.2 points but the Kings lost 1–4 to the Seattle SuperSonics in the First Round. In middle of the 2005–06 season, he became the first center since Sam Lacey in 1981 to record back-to-back double-doubles in both points and assists. After a career best 1,182 points scored during the season, the following 2006–07 season brought lower averages and totals of the previous five years. On April 10, 2007 Miller recorded his third career triple-double with 17 points, 10 rebounds and a career-high 11 assist.
On January 14, 2009, Miller recorded his first 30/20 game with 30 points and a career-high 22 rebounds in a win over the Golden State Warriors. Brad finished his five and a half seasons with the Kings, averaging just over 13 points, 8 rebounds and 4 assists a game.
On February 18, 2009, the Kings reached a tentative agreement to trade Miller and John Salmons to the Chicago Bulls for Drew Gooden, Andrés Nocioni, Michael Ruffin (later traded to Portland Trail Blazers for Ike Diogu) and Cedric Simmons. As a veteran presence on a young team, Brad added depth in the paint with forward/center Joakim Noah to compete in the 2009 NBA Playoffs after a two-year absence of post-season play while with the Kings. On April 28, Miller received a busted lip by Boston Celtics guard Rajon Rondo, and missed game-decisive free-throws at the end of game five of the Eastern Conference First Round. During game six of the 7-overtime series and after receiving 7 stitches for his lip, he posted a double-double with 23 points and 10 rebounds, shooting 8 for 9 from the floor. Miller averaged 10.3 points, 7.9 rebounds and 1.3 assists during the seven-game series in the 2009 Playoffs. He made 5 of 7 three point field goals (71.4%) and shot 79.2 percent from the free throw line.
On July 17, 2010, Miller signed a three-year contract with the Houston Rockets, worth $15 million. He was expected to back up Yao Ming and provide the Rockets a valuable insurance policy. On November 12, 2010, in Miller's first start after coming to the Rockets, he scored 23 points, grabbed 8 rebounds, and gave out 5 assists. On December 3, 2010, Miller tied his season-high 23 points, going a perfect 7-7 from the field, including 3-3 from downtown, and 6-7 from the foul line.
During the 2011 NBA Draft, Miller was traded to the Minnesota Timberwolves, along with the rights of Nikola Mirotić, ina deal that sent the rights of Donatas Motiejunas and Jonny Flynn to Houston. Due to microfracture knee surgery on his left knee while a member of the Rockets in May 2011, he was doubtful to begin playing for the Wolves at the projected start of the 2011-12 season (which was delayed due to the owners' lockout) - or indeed at all.
On January 12, 2012, Miller practiced with the team for the first time, strictly in half-court situations to protect his knee. He made his debut with the team on January 29, 2012. In an interview with Yahoo! Sports, he announced that the 2011-2012 season would be his final season. After the season, however, Miller's agent said that Miller was undecided about retiring.
On July 13, 2012, Miller was traded to the New Orleans Hornets, then traded to the Phoenix Suns as part of a three-team deal on July 27, 2012. He was waived by the Suns on August 15, 2012, when the team signed Jermaine O'Neal. Miller later reaffirmed his decision to retire.
Shortly after finishing his college career, Brad joined the US national team in the 1998 FIBA World Championship. During the time of the NBA lockout, there were no players from the league on the team. With fellow former Purdue standout Jimmy Oliver, Miller led the USA team to the bronze medal. He played under NBA coach Rudy Tomjanovich.
Miller was selected as a member of the U.S. squad that competed in the 2006 FIBA World Championship, where he played along with fellow NBA players, such as LeBron James, Carmelo Anthony and Dwight Howard. After much hype over the improvement of the team, the tournament ended in disappointment with a loss to Greece in the semifinal game. The team finished with the bronze medal by defeating Argentina. Despite pre-tournament assertions that the U.S. needed a good-shooting big man like Miller, he rarely played in the tournament and did not log any playing time in the decisive semifinal loss. The team was coached by Duke's head coach Mike Krzyzewski.