Run up to succeeding Blair,

In October 2004 Tony Blair announced he would not lead the party into a fourth general election, but would serve a full third term. Political controversy over the relationship between Brown and Blair continued up to and beyond the 2005 election, which Labour won with a reduced parliamentary majority and reduced vote share. The two campaigned together but the British media remained — and remains — full of reports on their mutual acrimony.

Blair, under pressure from within his own party, announced on 7 September 2006 that he would step down within a year. Brown was the clear favourite to succeed Blair for several years with experts and the bookmakers; he was the only candidate spoken of seriously in Westminster. Appearances and news coverage leading up to the handover were interpreted as preparing the ground for Brown to become Prime Minister, in part by creating the impression of a statesman with a vision for leadership and global change. Blair famously described Brown as the "great clunking fist", supposedly as a warning to his political opponents. Sceptics have said Blair's description was a deliberate attempt to label Brown as an unsubtle and one-dimensional policial operator.

Brown is the first prime minister from a Scottish constituency since the Conservative/SUP Sir Alec Douglas-Home in 1964. He is also one of only five prime ministers who attended a university other than Oxford or Cambridge, along with the Earl of Bute (Leiden), Lord John Russell (Edinburgh), Andrew Bonar Law (University of Glasgow), and Neville Chamberlain (Mason Science College, later Birmingham).

On 9 September 2006 Charles Clarke said in an interview that the Chancellor had "psychological" issues he must confront and accused him of being a "control freak" and "totally uncollegiate". Brown was also "deluded", Clarke said, to think Blair can and should anoint him as his successor now. Environment Secretary David Miliband stressed his support for Brown.

From January 2007 the media reported Brown had now "dropped any pretence of not wanting, or expecting, to move into Number 10 in the next few months" — although he and his family use the more spacious 11 Downing Street. This enabled Brown to signal the most significant priorities for his agenda as Prime Minister; speaking at a Fabian Society conference on 'The Next Decade' in January 2007, he stressed education, international development, narrowing inequalities (to pursue 'equality of opportunity and fairness of outcome'), renewing Britishness, restoring trust in politics, and winning hearts and minds in the war on terror as key priorities.

In March 2007 Brown's character was attacked by Lord Turnbull who worked for Brown as Permanent Secretary at the Treasury from 1998 to 2002. Turnbull accused Brown of running the Treasury with "Stalinist ruthlessness" and treating Cabinet colleagues with "more or less complete contempt". This was especially picked-up on by the British media as the comments were made on the eve of Brown's budget report.