Born in Adelaide, South Australia, Maher was spotted playing for the Sturt Sabres in the Australian Basketball Association where his outstanding form saw him earn a contract with the Adelaide 36ers. He took up an Australian Institute of Sport scholarship between 1989-1991. It turned out to be a great pickup for the 36ers as he would spend eighteen seasons with the club, thirteen as club captain. Including finals games, Maher played 526 games for the 36ers between 1992 and 2009, averaging 16.9 points, 4.2 assists and 4.3 rebounds per game. He made his debut for the 36ers on 4 April 1992, the same night as the opening of the 36ers new home the Clipsal Powerhouse. On the night Maher scored 11 points, grabbed 7 rebounds and handed out 4 assists to help the team to a 106-84 win over the North Melbourne Giants.
By 1994, Maher was regarded as one of the NBL's best guards and with the addition of the leagues 1993MVPRobert Rose to the 36ers roster, the team, now coached by former NCAA coach Mike Dunlap, would make its first Grand Final in eight years. Unfortunately for Maher and the 36ers they were defeated 2-0 in the Grand Final series by the North Melbourne Giants. He averaged 16.5 points, 5.5 rebounds and 2.5 assists over the series while averaging 13.3 points, 4.4 rebounds and 3.1 assists over the season.
Brett Maher took over from Mark Davis as captain of the 36ers at the start of the 1997 NBL season, and from 1998 under the coaching of Adelaide and Australian basketball legend Phil Smyth, Maher played an integral role in three of the four Adelaide 36ers NBL championships (1998, 1998–99 and 2001-02) and has also been the 36ers club MVP on six occasions. He was selected in 4 NBL All-Star Games (1996, 1997, 2005 and 2006) and he has been named in the All-NBL First Team in 2000 and 2003, All-NBL Second Team in 1997, 1998 and All-NBL Third Team in 1999, 2002. He also won the Larry Sengstock Medal for being the Grand Final MVP in 1999 and 2002. Maher is one of only two players to ever win the NBL Grand Final MVP twice, the other being Ricky Grace of the Perth Wildcats who won the award in 1990 and 1993.
On 7 February 2009 in front of a sellout crowd in excess of 8,000, the main court of The Dome was renamed The Brett Maher Court in honor of Maher who was playing his last home game before retiring from the NBL at the end of the 2008-09 season. The court that now bears his name is the only home court that Maher ever played on during his NBL career as the 36ers had moved to the then named Clipsal Powerhouse from their former home at the Apollo Stadium the same year that Maher started with the club.
The Brett Maher Court, February 2011
Maher has also been honored as one of only two players to have their number retired by the Adelaide 36ers. His #5 singlet hangs high at the Adelaide Arena alongside the #33 of former club captain, league MVP and long time team mate Mark Davis, who like Maher, played his entire NBL career with the 36ers. The pair were team mates in the 36ers 1998 and 1998-99 championship wins and Maher took over the club captaincy from Davis in 1997.
Brett Maher retired as the Adelaide 36ers all time leader in: games played (526), points (8,941), field goals (3,140), field goals attempted (7,072), three points made (1,162), three point attempts (2,835), assists (2,267) and steals (703). He is one of only four players to have won 3 or more NBL championships with the 36ers alongside Mark Davis, Paul Rees and Rupert Sapwell, and one of only two 36ers championship winning captains along with American import Bill Jones who captained the club to its first title in 1986.
Since retiring, Maher now also co-hosts an Internet Television show on Australia Live TV about basketball with former 36ers championship winning team mate Kevin Brooks called Inside the Game  shown on Fridays 6-7pm CST and the episodes are on AustraliaLiveTV.com. He is also the expert local analyst for 36ers NBL games televised on One HD and Network Ten that are played in Adelaide.
Brett Maher was named as the Adelaide 36ers Community Services Manager before the start of the 2013–14 NBL season.
Brett Maher is married to Tanya, and had three children, Cheyenne, Hudson and Indiana. In 2003 Hudson was diagnosed with a rare bone marrow disease called haemophagocytic lymphohistiocytosis (HLH) when just 3 months old and has since died, spurring the founding of The Hudson Maher Foundation that Brett Maher hopes can stop the disease from becoming more common.