Speaking at the close of the NATO Summit in Lisbon, the PM said Afghan forces would begin taking charge of security from early next year.
Transcript: Press conference at NATO Summit
He said the process would be complete by the end of 2014 allowing British troops to step back from combat roles by 2015.
The commitment we have entered into today to transfer the lead responsibility for security to the Afghan government by the end of 2014 will pave the way for British combat troops to be out of Afghanistan by 2015,” he told an end-of-summit press conference.
This is a firm deadline that we will meet.
Mr Cameron’s comments come after leaders of NATO’s 28 states backed a strategy to transfer leadership for the fight against the Taliban to Afghan forces by the end of 2014.
Afghanistan President Hamid Karzai attended the Summit, where he signed a long-term security partnership with NATO.
Mr Cameron hailed today’s agreement as the beginning of a “new phase in the campaign”.
This is a commitment made at the very highest level, with the broadest possible international support.
While UK forces would no longer be involved in combat duties by 2015, Mr Cameron said NATO had also agreed to provide long-term support for Afghanistan on training, diplomacy and development.
We will stand by Afghanistan for many years to come.
On Friday member states agreed a new 10-year “strategic concept”, a document that defines the fundamental nature of NATO’s role in the world.
The document commits NATO members “to defend one another against attack, including against new threats to the safety of our citizens”, without defining a geographical limit to its theatre of operations.
Also at the Summit, Russia agreed to co-operate on NATO’s programme to defend against ballistic missile attacks.
NATO Secretary General Anders Fogh Rasmussen said the two sides had agreed in writing that they no longer posed a threat to one another.
Speeches and transcripts: Press conference at NATO Summit