Brown led the Australian Greens from the party's foundation in 1992 until April 2012, a period in which polls grew to around 10% at state and federal levels (13.1% of the primary vote in 2010).

In October 2003 Brown was the subject of international media interest when he was suspended from the parliament for interjecting during an address by United States president George W. Bush.

During his tenure at the hospital, he and other senior medical staff took a pacifist stance by refusing to certify young men who did not wish to fight in the Vietnam War as fit to be conscripted.

On the day of his release in 1983, he became a member of Tasmania's parliament for the House of Assembly seat of Denison after the Democrats MP Norm Sanders resigned to successfully stand for the Australian Senate;[15] Brown was elected to replace him on a countback.

During his first term of office, Brown introduced a wide range of private member's initiatives, which include freedom of information, death with dignity, lowering parliamentary salaries, gay law reform, banning the battery-hen industry and advocation for nuclear free Tasmania.

[footnote 1] He agreed to support a minority Labor Party government, on the basis of a negotiated Accord (signed by Michael Field and Bob Brown) in which the Green independents agreed to support the budget but not motions of no confidence, and the ALP agreed to develop a more open parliamentary process, to consult on departmental appointments, provide a legislative research service, parity in parliamentary staffing and a reform agenda which included equal opportunities, freedom of information, national parks protection and public disclosure of bulk power contracts and royalties from mining companies.

He also introduced bills for constitutional reform, forest protection, to block radioactive waste dumping, to ban mandatory sentencing of Aboriginal children, to prohibit the use of cluster munitions and for greenhouse abatement.

At the 2001 federal election Brown was re-elected to the Senate with a greatly increased vote, and was outspoken on Prime Minister John Howard's refusal to allow 438 asylum seekers (mostly from Afghanistan) to land on Christmas Island after they had been rescued from their sinking boat in the Indian Ocean by the MV Tampa, a Norwegian freighter.

When President Bush visited Canberra on 23 October 2003, Brown and fellow senator Kerry Nettle interjected during his address to a joint sitting of the two houses of parliament.

[19] During Bush's speech Brown and Nettle wore signs referring to David Hicks and Mamdouh Habib, two Australian citizens held at Guantánamo Bay, Cuba, at that time (Habib was later released without charge and Hicks served a prison term for providing material support for terrorism), following their apprehension by United States forces in Afghanistan and Pakistan respectively.

Gunns ultimately failed with the company finally dropping all claims against Brown on 13 December 2006[21] while continuing its case against others including The Wilderness Society.

In early 2007, Brown attracted scorn from sections of the media and the major political parties for his proposal to commit to a plan within three years, that would eventually see the banning of coal exports.

Following his re-election and that of the new Labor Government, Brown called on the new Prime Minister, Kevin Rudd, to set fixed carbon targets immediately, and to announce their levels at the upcoming United Nations Bali Climate Change Conference in December 2007, continuing his climate campaigning, and saying that it was "obvious" what the outcome would be if Australia was to not set carbon emissions goals.

Bob Brown brought a case against Forestry Tasmania citing threats to endangered species like the Swift parrot and Wielangta Stag Beetle.

[27] On appeal to the full bench of the Federal Court level, the case was lost, without rejecting the earlier judgement that logging would further endanger these species.

[33] On 9 June 2009, Australian entrepreneur Dick Smith promised to help bail him out if necessary,[34] an offer that was not needed after pledges of support from over 1,000 donors covered Brown's legal bill within a few days of his announcement.

[35] In 2011, after the 2010–11 Queensland floods Brown drew criticism for suggesting that half the Mineral Resource Rent Tax be allocated to future natural catastrophes.

Held at Federation Square in Melbourne, the concert was part of a long-running campaign to protest against a proposal to industrialise the James Price Point area in Broome, Western Australia.

[56][citation needed] A march to protest the proposed gas refinery construction at James Price Point accompanied the free concert and campaign supporters were photographed with banners and placards.

In October 2017 the High Court agreed, by a majority although for differing reasons, that the provisions were invalid in that they breached the constitutional freedom of political communication.

[66] In July 2019 Brown came out strongly opposing a large wind farm to be set up in Northern Tasmania, raising concern for bird species.

[79] As of 2018[update] Brown lived in Eggs and Bacon Bay, Tasmania, with his long-time partner, Paul Thomas, a farmer and activist whom he met in 1996.

[82] In an interview with Richard Fidler on ABC radio, Nigel Brennan, an Australian photojournalist who was kidnapped in Somalia and held hostage for 462 days, revealed Brown had contributed $100,000 of his own money to help pay the ransom for his release.

[citation needed] It was also revealed that Brown contacted Australian businessman Dick Smith asking that he also contribute funds towards the release of Brennan.

[84][85] Brown has published several books including Wild Rivers (1983), Lake Pedder (1986), Tarkine Trails (1994), The Greens (1996) (with Peter Singer), Memo for a Saner World (2004), Valley of the Giants (2004), Tasmania's Recherche Bay (2005), Earth (2009), In Balfour Street (2010) and Optimism: reflections on a life of action (2014).