 Mr Brown is paying his fourth visit to Iraq as PM |
Gordon Brown and Iraqi prime minister Nouri Maliki say UK forces will have "completed their tasks" and leave the country by the end of July next year.
The two leaders' joint statement came as they held talks in Baghdad.
They also said the partnership between the two countries would continue. It is Mr Brown's fourth trip to Iraq as PM.
The visit by Mr Brown, who is travelling with Chief of the Defence Staff, Air Chief Marshall Sir Jock Stirrup, was not announced in advance.
'New era'
At a press conference, Mr Brown said: "We have agreed today that the mission will end no later than the 31 May next year.
"Our troops will be coming home within the next two months (after that)."
He went on: "The biggest reduction will be at the end part of the period we are talking about."
Mr Maliki confirmed that the agreement included a provision for the Iraqi government to request an extension of the British military presence.
However, both leaders indicated that it was not expected to be used.
There are currently about 4,100 UK troops serving in Basra, southern Iraq.
In their joint statement, Mr Brown and Mr Maliki said: "The role played by the UK combat forces is drawing to a close.
"These forces will have completed their tasks in the first half of 2009 and will then leave Iraq."
They added: "The partnership between the two countries will continue to take on new dimensions and will be strengthened through cooperation in all areas due to the prominent position of the UK within the EU and the United Nations Security Council.
"This relationship of cooperation and friendship between Iraq and the UK is entering a new era and will yield continuing cooperation that will last for many years to come."
BBC defence correspondent Paul Adams said the withdrawal of UK troops was expected to start in the spring and that 200 to 300 military advisers were likely to remain in place to help the Iraqi government.
