MPs have voted in favour of staging air strikes in Iraq to combat Isis (now known as Islamic State) by an overwhelming majority of 481, with 524 voting yes and 43 voting no.
Britain will now join the US-led coalition taking part in miltary action against IS, along with France and "partner nations" from the Arab world - Bahrain, Saudi Arabia, Jordan, Qatar and the United Arab Emirates.
Belgium and Denmark have also announced they will join the coalition in launching air strikes against the militant group.
Earlier, after Cameron had recalled Parliament to discuss how to confront IS, he told MPs military action was the only way to deal with the "psychopathic terrorists that are trying to kill us".
He added: "We have to realise that, whether we like it or not, they have already declared war on us.
"There isn't a 'walk on by' option. There isn't an option of just hoping this will go away."
Cameron also said the result of the 2003 invasion of Iraq should not overshadow the intentions of the coalition in their fight against IS.
He said: "This going to be a mission that will take not just months but years, but I believe we have to be prepared for that commitment. And the reason for that is that America, Britain and others are not contemplating putting combat troops on the ground."
Cameron told the House of Commons that all military decisions will be a result of "patience and persistence, not shock and awe" — a direct reference to the phrase associated with the invasion of Iraq.
Speaking to Commons at the end of the six-hour debate, Deputy Prime Minister Nick Clegg urged that "we must act" to defeat IS, but must be "mindful of the mistakes and lessons of the past".
Labour leader Ed Miliband said people are right to be of wary military action in Iraq following the 2003 invasion but said Britain could not consider the alternative to "turn away".
He added: "I know that because of the 2003 Iraq war people will be fearful about this. We're determined we don't repeat the mistakes of the past but equally we don't turn away from the threats that we face."
It has emerged Shadow Education Minister Rushanara Ali resigned from Labour's front bench in order to abstain from the vote to decide on military action.