The prime minister said in terse comments while he believes in a "tough response" to the use of chemical weapons, he would respect the will of the House of Commons.
At the start of the week, Cameron had seemed ready to join Washington in possible military action against Assad over the alleged chemical weapons attack. But the push for strikes against the Syrian regime began to lose momentum as Britain's Labour Party — still smarting from its ill-fated decision to champion the invasion of Iraq in 2003 — announced its opposition to the move.
Cameron gave concessions, promising to give the U.N. inspectors time to report back to the U.N. Security Council and to do his outmost to secure a resolution there. He also promised to give lawmakers a second vote in a bid to assuage fears that Britain was being rushed into an attack on Assad.
In the end, it wasn't enough to dispel lingering suspicions that what was billed as a limited campaign would turn into an Iraq-style quagmire.
Tony Travers, the director of the government department at the London School of Economics, said Cameron had clearly miscalculated when he brought Parliament back early from its summer recess. He said the move had been unpopular even within Cameron's Conservative Party.
"Clearly this will be seen as a defeat, it suggests he got the politics wrong, both with the opposition and with some members of his own party," Travers said. "It's not great, it's not brilliant, nor is it the end of the world for him. He's lost votes before. It doesn't necessarily stop them taking further action, but they are going to have to start again really."
He said there was "not a lot" of public support for British military activity in Syria.