The chapel was built in 1951, with the support of then Prime Minister Winston Churchill, to celebrate the effort and sacrifice of pilots in the Battle of Britain.
The government had confirmed it was stopping its annual funding of £50,000 for the chapel, however London Biggin Hill Airport agreed to make up this shortfall every year instead.
Biggin Hill was one of the key airbases for British fighter planes protecting London and South East England during the Battle of Britain.
Speaking during Prime Minister's Questions, Mr Cameron said: "I can absolutely confirm to the House that this chapel will be preserved for future generations, as we've always recognised its importance and its rich heritage.
"I think in all the great moments of British history it is possibly the case that the Battle of Britain 1940 stands out as one of the most important times there have been, so we will protect this chapel and do whatever it takes to protect it for future generations."
The Battle of Britain happened in 1940, against German and British aircraft. Britain won the battle, which forced Adolf Hitler to cancel a planned land and air invasion on the country.
Because Hitler could not significantly weaken Britain's air defences, or strike a ceasefire or surrender from them, the Battle is known as a major German defeat and turning point in the Second World War.