Gordon Brown arrived at Baghdad International Airport on Tuesday for his first visit to Iraq since becoming prime minister.
Mr Brown arrived under heavy guard alongside Christopher Prentice, the British ambassador in Iraq.
The prime minister was then taken by helicopter to the heavily fortified Green Zone to meet his Iraqi counterpart Nouri Maliki.
Mr Brown was in talks with Mr Maliki for an hour. He was also due to meet the US commander in Iraq, General David Petraeus.
Aside from politicians and military chiefs, Mr Brown also spoke to ordinary British troops serving in Baghdad. They are among 5,500 UK personnel in Iraq at present.
Mr Brown also met Air Chief Marshal Sir Jock Stirrup, Chief of the Defence Staff. He later announced that 1,000 troops would return home from Basra by the end of this year.
Mr Brown also confirmed that Basra province could be handed over to full Iraqi control in the next two months.