The Foreign Secretary says other countries need to step up contributions to stop Islamic State spreading to Europe.
Mr Hammond was speaking ahead of a London meeting of foreign countries, including US Secretary of ministers from 21 countries.
Speaking at Downing Street he said: “The threat from extremist terror you face in Iraq is also a threat we face here in the United Kingdom.”
Mr Hammond told Sky News it was crucial that Britain was involved in the fight against IS, also referred to as ISIL.
He said: “Clearly the reason we are doing this is to keep our own country safe.
“The defence of our homeland begins by supporting the Iraqi government and the Iraqi people in the fight against ISIL.”
Mr Hammond said progress had been made and the advance of Islamic State had been halted.
He added: “We have always said this is going to be a long job.
“This isn’t going to be done in three months or six months – it’s going to take a year, two years to push ISIL back out of Iraq – but we are doing the things that need to be done in order to turn the tide against ISIL.”
Thursday’s conference, which comes after the French terror attacks in which 17 people were killed, will discuss ways to cut off IS finances and stop it recruiting foreign fighters.
US-led coalition forces have carried out more than 1,000 airstrikes inside Iraq – around 100 conducted by RAF aircraft.