Brown moved to Tasmania in 1972 and worked as a general practitioner in Launceston. He soon became involved in the state's environmental movement, in particular the campaign to save Lake Pedder. By 1972, he was a member of the newly formed United Tasmania Group, Australia's first "green" party. In 1976, he fasted for a week on top of Mt Wellington in protest against the arrival at Hobart of the nuclear-powered warship . In 1978 Brown was appointed director of the Tasmanian Wilderness Society. In the late 1970s he emerged as a leader of the campaign to prevent construction of the Franklin Dam, which would have flooded the Franklin River valley as part of a hydroelectricity project. Brown was among the 1500 people arrested while protesting during the campaign. He subsequently spent 19 days in Hobart's Risdon Prison. 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; Brown was elected to replace him on a countback. The Franklin campaign was a success after Federal government intervention protected the Franklin River in 1983. 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. His 1987 bill to ban semi-automatic guns was voted down by both Liberal and Labor members of Tasmania's House of Assembly, nine years before the Port Arthur massacre resulted in a successful federal Liberal bid to achieve the same results. 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 leader. 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. This agreement, however, 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.