Born the son of a Church of Scotland minister in 1951, Brown was fast-tracked into Edinburgh University aged just 16, where he suffered a rugby accident which blinded him in one eye and required lengthy treatment to save the sight in the other.
While working as a politics lecturer and journalist, he fought his way into a prominent position in the Scottish Labour Party, arriving at Westminster in 1983 as MP for Dunfermline East. He was swiftly spotted as a rising talent, joining the front benches within two years and rising to shadow chancellor in 1992.
After the surprise death of John Smith in 1994, he was viewed by many as a natural successor. But he struck a deal with Tony Blair, under which the more presentationally-talented younger man would take the leadership in return for a promise of control over economic policy and an eventual handover of power.
Together, the two men forged the New Labour machine which triumphed in 1997 and dominated UK politics for the following decade. But the deal carried in it the seeds of their future rivalry, with apparently reliable reports of furious rows behind the scenes in Downing Street as Mr Brown demanded that Mr Blair name a date for the succession.
Meanwhile, Mr Brown married PR executive Sarah Macaulay at the age of 49. The couple faced heartache in their family life, as first child Jennifer died after just 10 days in 2002 and second son Fraser was diagnosed with cystic fibrosis.
After 10 years at the Treasury, where he earned a reputation as the "Iron Chancellor" who claimed to have ended boom and bust, Mr Brown finally replaced Mr Blair at 10 Downing Street on June 27, 2007.
Supporters hailed him as the "big clunking fist" who would crush any opposition at the despatch box, but Tories demanded an instant election for the unelected PM to seek a mandate. Brown was branded a "ditherer" when he chose not to and Labour slumped in the polls to levels last seen under Michael Foot's disastrous leadership.
Brown's reputation wavered during the financial crisis but was boosted when he played an important part in the worldwide bank bailout. The expenses scandal then cast a pall over his premiership, even if he did not personally face serious charges and opponents soon revived an anonymous claim that Brown was "psychologically flawed". Bloggers also mocked him for his awkward smile and his hapless attempts to get to grips with modern technology like the internet.
Despite setbacks which would have shaken a less determined man, Brown showed no sign of giving in. He led international agreement at the London Summit to tackle the downturn and cemented a surprising new alliance with former enemy Peter Mandelson after a series of leadership challenges. Meanwhile, wife Sarah was brought into the public eye to show the softer side of a politician who has always seemed uncomfortable talking about his personal life.