Bob Brown ends his long and successful parliamentary career with the Greens at the peak of their power.

The former medical practitioner has travelled the long journey from the United Tasmania Group, which won just under 4% of the vote in the 1972 state election, to leader of the party with the balance of power in the Senate, a deal with a minority government and a House of Representatives seat.

After a medical career, Brown served 10 years in the Tasmanian parliament (taking his seat the day after he was released from prison for protesting against the Franklin Dam) and, as he would do in the Senate, oversaw the rise of the Greens to balance-of-power status in Tasmania.

Brown entered the Senate in 1996 and was, from 1998 to 2001, the sole Greens representative (and parliament’s first openly gay member). A decade later, he leaves the Senate with nine Greens senators, after the Greens Senate vote reached 13% in 2010.

At a time when politics is increasingly professionalised and parties are pushing younger, less experienced people into senior positions, Brown was a traditional conviction politician, forthright in attacking the most sacred of cows in Australian public policy on economics, the media and foreign policy, including challenging George W. Bush when he addressed Parliament. He most recently attracted criticism for his now-famous “fellow earthians” speech arguing for a global parliamentary democracy.

What was missed by most commentators was that the speech was to a Greens party conference; when Barnaby Joyce plays to his party’s base it is seen as canny retail politics; when Brown did the same, it was “looney left” stuff.

A key challenge from the rise of the Greens to balance of power status (and the spread of Greens senators to all states) has been managing expectations from the party’s base — which varies significantly in different states, with the Australian Greens still notionally being a composite of separate state parties. But this was deftly managed in relation to the carbon price with Christine Milne convincing Labor to establish an all-party process to develop a package, enabling the Greens to shape the package from the outset, which led to a significant array of “direction action” measures, including a massive Clean Energy Finance Corporation investment vehicle.

The result is that, so far, the threat of alienating the party base through the necessary compromises that come from the balance of power has yet to eventuate. “I’ve always waited for a protest outside our window saying we’re too weak,” Brown told Crikey recently, “but I find myself in a situation where we’re taking a stronger stand on environmental issues than key mainstream long-established environment group — I never thought I’d find myself in that position.”

Despite media portrayals of him as a soft liberal, Brown’s early political experience was torrid.

“Twenty years ago I could not go up the street without getting abused,” he said. “Quite a lot of it was homophobic abuse, but it was coming out of the fact that I was an environmentalist, wanting to change the economic direction, the skill set and the employment base of this state … it was threatening, it was abusive, it was foul language, car windows down when people drove up the street … having the personal wherewithal to go through that sort of ever-present abuse … is a bit of a crucible for toughening up and a bit of a learning curve.

“But,” he added, “I’m not in Syria.” And, he says, now he has the opposite problem of being stopped by well wishers.

With the carbon pricing package about to start and the party at historic levels of strength federally, Brown leaves politics as the most successful non-major party politician of his generation, having twice built up a parliamentary third-party presence to balance-of-power levels.

Brown’s Tasmanian colleague Christine Milne will succeed Brown; like him, Milne has considerable state parliamentary experience and led the Tasmanian Greens in coalition with the Liberals in the 1990s (after succeeding Brown). It was Milne who drove the Greens’ involvement in the carbon pricing package.

But she is less of a party icon than Brown, and the Greens will be closely watched to see whether the leadership transition sees more fractures within a diverse party room and membership.

University of Tasmania economist Peter Whish-Wilson, who was second on the Greens Tasmanian Senate ticket at the 2010 election, is the likely replacement if he wants Brown’s spot; Whish-Wilson is highly regarded within the party.

Brown today rightly declared himself proud to be leaving the leadership of a growing party. But he is less optimistic about the overall direction of progressive politics currently.

Progressive politics, he told Crikey, is in a “stunning and very troubling retreat … it’s being totally eclipsed by the power of the corporations … I see this disconnect where people are so frustrated with politics generally that they don’t see that there’s any hope in the political arena whereas there is no hope anywhere else.

“The simplistic dictum I have is democracy or guns, take your pick, and if you’re gonna be in a community movement, you have to relate to the politicians.”