Bob Brown was born in Oberon, New South Wales and graduated in medicine from Sydney University. He moved to Tasmania in 1972 and worked as a general medical practitioner in Launceston. He soon became involved in the state's environmentalist movement, in particular the campaign to save Lake Pedder, and was a member of the United Tasmania Group in 1972, Australia's first "green" party. In a newspaper interview at this time, Brown "came out" as gay.
In 1978 Brown was appointed director of the Tasmanian Wilderness Society. In the early 1980s he emerged as a leader of the campaign to prevent construction of the Franklin Dam, which would have drowned the Franklin River valley as part of a hydroelectricity project. The campaign was a success, and in 1983 Brown was elected to the Tasmanian Parliament as its first Green member.
In 1989 Tasmania's system of proportional representation allowed the Greens to win five out of 35 seats in the Tasmanian House of Assembly, and Brown became their unofficial leader (the Greens do not have formal leadership positions). He agreed to support a minority Labor Party government, but this agreement broke down over forestry issues in 1992. In 1993 Brown resigned from the House of Assembly and stood unsuccessfully for the federal House of Representatives.
Brown was elected to the Australian Senate for Tasmania in 1996, and was an outspoken voice in opposition to the conservative government of John Howard, and in support of green and human rights issues, including international issues such as Tibet, East Timor and West Papua.
During his parliamentary career in Tasmania, Brown was not particularly outspoken on gay rights issues, although he never concealed the fact that he was gay. In federal Parliament, however, he became more active on this issue, particularly when a second gay Senator, Brian Greig of the Australian Democrats, was elected in 1998.
At the 2001 federal election Brown was re-elected to the Senate with a greatly increased vote, and became recognised as the national leader of the anti-war and anti-American left. He was particularly vocal in his opposition to Australian participation in the 2003 invasion of Iraq.
Despite his rather dour and humourless public manner, he is widely admired as a man of courage and conviction, even by those who disagree with him. One example of Brown at his most tolerant (as well as an indication of a dry sense of humour) is his welcoming of anti-gay campaigner Fred Nile's intention to run as a Christian Democratic Party of Australia candidate for the Australian Senate in the next federal election. Brown was quoted as saying "He will give the opportunity to highlight the Greens' humanitarian policies which have doubled the vote for the Greens in the last three or four years."
When President Bush visited Canberra on 23 October 2003, left-wing members of the Labor Party decided to present him with a letter setting out their opposition to the Iraq war, but not to disrupt his speech. Only Brown and Nettle took their opposition to the point of interjecting during his address to a joint sitting of the two Houses of Parliament. During Bush's speech Brown and Nettle wore signs referring to David Hicks and Mamdouh Habib, two Australian citizens currently being held at Guantanamo Bay, Cuba, following their apprehension by United States forces in either (this is disputed) Afghanistan or Pakistan. After the speech, however, Brown shook Bush's hand.
Bush accepted the interjections with good humour, but the Speaker of the House, Neil Andrew, formally "named" Brown and Nettle and they were suspended from the Parliament for 24 hours which prevented them from being present for -- and making similar interjections during -- a similar address from Chinese Presdient Hu Jintao the next day.