In November 2017, he returned to the Senate as a member of the Australian Greens, replacing Larissa Waters after her disqualification during the parliamentary eligibility crisis.

He then worked as an electorate officer for Queensland Democrats senators Cheryl Kernot and John Woodley between 1990 and 1997.

In 2004, he cried in the Senate chamber over a proposed law to define marriage as between a man and a woman, which he called an "absolute disgrace".

[4] To a degree, Bartlett stabilised the Democrats' troubled party room and spoke strongly against the Government's maltreatment of refugees and maladministration of the Department of Immigration.

He also oversaw the Democrat senators' use of their potential balance of power role to influence increased funding for Medicare, protection of the welfare payments of sole parents, the unemployed and the disabled, and entitlement of some homosexual couples to superannuation entitlements equivalent to those enjoyed by heterosexual couples.

"[citation needed] Bartlett resumed the party's parliamentary leadership in January 2004, giving an assurance that he would totally abstain from alcohol.

In May 2012, Bartlett ran for the Lord Mayoralty of Brisbane for the Greens, receiving 10.7% of the primary vote, a 2.3% increase on the previous election.

Speaking as a former Democrats leader, Bartlett reflected that the party's support of the Howard Government's introduction of the GST was "politically catastrophic", but the "last straw" for the party was the demise of Stott Despoja as leader in 2002:[11] Even though the Democrats eventually disappeared from parliament in 2008, basically our political support crashed and burned in 2002.Bartlett was again endorsed by the Greens as a Senate candidate for Queensland at the 2016 federal election.

[12] While he did not meet the quota for election, his colleague Senator Larissa Waters resigned her position on 18 July 2017 after discovering she held dual Australian and Canadian citizenship.

[17] As announced, Bartlett contested the Division of Brisbane in the House of Representatives at the 2019 federal election receiving 22% of first preferences.

[18] After departing parliament, Bartlett took up a position as a part-time Research Fellow with the Migration Law Program at the Australian National University.