He said "our job is to stand with the thousands of people who are fighting for democracy" in Iraq and Afghanistan.
"I think anything else would be a very, very great mistake for this country's security and the wider world," he said.
Mr Blair made the comments during a questions session at the GMB union's conference after a delegate urged him to bring British troops home now.
| I believe now, with the attack on the democratic forces in Iraq, our job is to stand with them until the job is done Tony Blair |
Mr Blair said he had "never disrespected" people opposed to the war, but urged them to listen to the voices in the new democratic Iraqi government, which is made up of Shias, Kurds and Sunni members.
He said terrorists in Iraq were "trying to stop them having the same rights we have to elect their government", to equality and to freedom.
"Those people are fighting a struggle that I think concerns us as well," he said.
"I believe now, with the attack on the democratic forces in Iraq, our job is to stand with those people who are fighting for democracy, stand with them in Iraq, stand with them in Afghanistan and stand with them until the job is done."