He completed a Bachelor and a Master of Arts in political science at the University of Auckland. He enjoyed and participated in student politics, including becoming a member of the New Zealand Greenpeace executive that sent Greenpeace III to Mururoa Atoll in 1972 in the campaign against French nuclear testing in the Pacific Ocean. As a member of Princes Street Labour, he also spent considerable time working on New Zealand Labour Party campaigns including that of Mike Moore. After university, Rann was a political journalist for the now defunct New Zealand Broadcasting Corporation. It was reported that he struggled with being an objective reporter.
Rann attended his brother's wedding in Adelaide, South Australia, in 1977, and shortly afterwards moved there to accept a position with Premier Don Dunstan's Unit for Industrial Democracy. He worked for Dunstan as his press secretary, speech writer and adviser, and went on to serve Labor premiers Des Corcoran and John Bannon in the same capacities after Dunstan's retirement from politics.
One commentator reports that Rann was "frankly inspired by Dunstan's idealism" as opposed to "Bannon's cool electoral pragmatism". Rann sometimes talked during this period of his ambitions to one day become Premier. Rann wrote speeches on and assisted in policy development for civil liberties, land, gay and women's rights, and opposition to uranium mining, revealing a vein of idealism, his early predilection was left of centre.
When Briggs was abolished in an electoral redistribution, Rann was elected to the new seat of Ramsay at the 1993 election. At the election, Labor lost government in a landslide due to the State Bank. Rann was promoted to deputy leader of his party following the defeat, however Arnold resigned as leader in September 1994. Rann became leader with the support of Labor Right powerbroker Don Farrell, who promised Rann two terms in the position. Rann achieved a 9.5 percent two party preferred swing to Labor in the 1997 election, narrowly failing to win government.
Rann remained Leader of the Opposition until the 2002 election, at which he won enough seats to form a government and become Premier on 6 March 2002 with the support of an independent MP, Peter Lewis. Lewis' decision was controversial, but Rann later secured the support of conservative independent Rory McEwen and the Nationals' Karlene Maywald by adding them to his cabinet, and Bob Such as speaker.
In addition to Premier, Rann is also the current Minister for Economic Development, Minister for Social Inclusion, Minister for the Arts, and Minister for Sustainability and Climate Change.
Rann was appointed chairman of a new Australian Federation Council in July 2006, a council which aims to improve state-federal ties. Rann also ran for national presidency in the National Executive in August 2006, and made senior-vice presidency on 27% of the vote. He began a rotation as National President on 1 March 2008.
Although seen as pragmatic rather than reformist, some commentators point to innovative policies in his governments creation of boards, from the presidential nature of the boards' appointment, to their independence from government, to their roles as monitors of policy progress. As such, Rann is sometimes considered closer to Dunstan than to Bannon.
Rann has also personally likened his government to Dunstan's, stating "I'm a totally different person to Don Dunstan, but in the '70s for different reasons South Australia stood head and shoulders above the crowd. We stood out, we were leaders. Interestingly, the federal Government is setting up a social inclusion unit based on ours. Again it's about us not only making a difference locally, but being a kind of model for others, which is what Dunstan used to say he wanted us to be ... a laboratory and a leader for the future." Rann says he expects other reforms to be based upon those enacted under his government, citing the state's strategic plan, a 10-year framework for development for government and business, of which the New South Wales government will be adopting. "It's a plan for the state, not just promises at each election. A lot of colleagues interstate thought I'd gone mad when we named targets. Well we didn't want to set targets we could easily pass and then pat ourselves on the back for, what's the point of that?
Rann has been a very popular Premier with the best polls for a state government in the country, with his approach generally moderate and crisis free. Polling by Newspoll has seen Rann achieve a historic 64 percent as Preferred Premier, and 61 percent on the two-party preferred vote. However, fourth quarter 2007 polling marked a turning point for Rann's Labor government since the previous election, on 54 percent of the two party vote, a fall from the previous poll of five percent. Rann's Preferred Premier rating was at 50 percent compared to 25 percent for current Liberal leader Martin Hamilton-Smith. Third quarter 2008 polling saw a continued drop in the primary vote, down three to 38 percent, with the Liberal vote up five to 40 percent, breaking 50-50 after preferences - the Preferred Premier figure recorded a six-point drop to 48 percent for Rann and up three to 30 percent for Hamilton-Smith. Some commentators put the poll slump down to "labour movement ructions" over the underfunded WorkCover liability, and the River Murray.