It is understood the two men discussed global trade agreements and the continuing conflicts in Iraq and Afghanistan in talks lasting about 45 minutes.
The unplanned meeting came about when Mr Bush learned Mr Brown was in Washington to meet US national security adviser Stephen Hadley.
The chancellor is stateside to hold meetings with and fulfil commitments to the International Monetary Fund, the World Bank and G8.
Mr Blair has faced criticism in Britain for aligning the country's foreign policy too closely with that of the US, and the chancellor's relationship with Mr Bush will be a key indication of the direction he will take on the world stage should be become prime minister.
Following the backlash to March's Budget, Stalinists jibes and criticism over his decision to scrap tax relief on shares despite knowing it would create a £75 billion pensions black hole, Mr Brown and Labour in general have suffered in opinion polls over the last month.
In an interview with the Guardian published today, the chancellor denied that he was having a "rough time" of late.
"Not compared to the rough times I've had," he elaborated.
"I've never lost sight of the idea that the only point in politics is to see if you can make a difference and I hope, I hope, I don't forget that's what made me want to get into politics in the first place. I think you've got to ride the slings and arrows."
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