Bartlett was born in Brisbane, Queensland. He gained qualifications in social work from the University of Queensland, and later a Bachelor of Arts. He worked as a social worker for the Department of Social Security, and later for the community radio station 4ZZZ. He also played in a number of local bands, as a drummer.
Bartlett joined the staff of Senator Cheryl Kernot following her election to the Senate in 1990. He also served as the secretary of the Queensland Division of the Australian Democrats. Kernot became leader of the party in 1993 — at this time Bartlett moved to Senator John Woodley's staff. He was the Democrats' Queensland Campaign Director for the 1993 and 1996 elections.
In 1997, when Kernot resigned to join the Australian Labor Party, Senator Natasha Stott Despoja took her place as party leader, and Bartlett was appointed to the Senate vacancy caused by Kernot's resignation. After Stott Depoja's resignation in 2002, Bartlett won the leadership of the party by a 60% majority in a ballot of party members.
On December 6, 2003, Andrew Bartlett stepped down "indefinitely" as leader of the party, after an incident involving Liberal Senator Jeannie Ferris in the Senate chamber. Ferris said that Bartlett had stolen five bottles of wine from a Liberal Party function in Parliament House. When Ferris confronted Bartlett, she said, he grabbed her arm and called her a "fucking bitch", then followed her out of the chamber while verbally abusing her. Parliamentary video of part of the incident appeared to show that Bartlett was drunk in the chamber.
The next morning Bartlett did not deny any of Ferris's allegations. He said that his behaviour had been "totally unacceptable", and that he had apologised in writing to Senator Ferris, to the Senate, and to his party. The Democrats issued a statement stating that Deputy Leader Senator Lyn Allison would serve as the Acting Leader of the party. Bartlett's former employer, John Woodley, said in an interview that Bartlett had had a drinking problem for some time, something Bartlett himself appeared to confirm at a press conference.
In the week following the incident, senior Democrats including Senator Stott Despoja said that they thought Bartlett should formally resign as Leader. Others said that he should be given an opportunity to deal with his problems. On 12 December Bartlett announced that he would not resign. He gave his party an assurance that he would totally abstain from drinking.