In a news conference to mark the end of the London summit, the Prime Minister said the funding formed part of a package that would shorten the recession and save jobs.
Other measures included action to "clean up" the banks - with new rules on pay and bonuses - and measures to tackle tax havens.
"We believe that global problems require global solutions," he said.
Mr Brown said the leaders agreed a "new consensus" to do what was necessary to restore growth and jobs and to rebuild confidence and trust in the financial system.
"This is the day that the world came together to fight back against the global recession, not with words but with a plan for global recovery and reform," he said.
Mr Brown said new rules on pay and bonuses "at a global level" that reflected actual performance not failure would "encourage corporate responsibility in every part of the world".
A new "financial stability board" would "ensure co-operation across frontiers and to stop risk to the economy" and provide an early-warning mechanism, he said. For the first time, there would be a "common global approach to how we deal with impaired, or toxic, assets".
The "unprecedented fiscal expansion" already under way would mean a five trillion dollar injection by the middle of next year, he said, helping save or create millions of jobs.
Central banks had agreed to "maintain expansionary policies as long as they are needed using the full range of options available to them". But there would also be an additional one trillion dollars "made available to the world economy through the International Monetary Fund (IMF) and other institutions".