The men shared an office, forming a relationship that would come to change the direction of the Labour party.
Both served in the Shadow Cabinets of Neil Kinnock and John Smith and were seen as high-flyers.
But the death of Mr Smith marked a turning point in their relationship.
As home affairs spokesman, Mr Blair pushed for modernisation of the party and was favourite to win the leadership election, ahead of the then shadow chancellor Mr Brown and other potential rivals.
On 31 May 1994 the pair famously met at Granita restaurant in Islington, north London, where the then shadow chancellor is said to have agreed to step aside and give Mr Blair a clear run for the top job.
The other part of the bargain, that Mr Blair would one day stand down in favour of Mr Brown, was made into a TV drama The Deal.
The rivalry between the pair became a source of great interest, particularly after Labour's landslide 1997 election victory. Relations appeared particularly strained when, in 1998, Mr Blair's press chief Alastair Campbell reportedly described the chancellor as "psychologically flawed".
Reports that Mr Blair and Mr Brown were barely speaking surfaced in the run-up to the 2005 election.
A new level was reached on in autumn 2006, when there were reports of Mr Blair and Mr Brown having an "acrimonious meeting" over the succession issue. This was followed by the resignation of a junior minister and seven government aides who had urged Mr Blair to stand down in an attempted coup.