He said in the interview that the threat Saddam posed to the region was uppermost in his mind and the possibility that Iraq had powerful weapons was only one factor behind his decision.
Others were Saddam's 12 years of stalling United Nations weapons inspectors and his use of chemical weapons on his own people.
Blair said he understood some people opposed his decision, and parents of some of the British service personnnel killed there were angry.
"I sympathise with the people who were against it for perfectly good reasons and are against it now, but for me, you know, in the end I had to take the decision."
Tony Blair, former UK prime minister
"I sympathise with the people who were against it for perfectly good reasons and are against it now, but for me, you know, in the end I had to take the decision," he said.
"There is no point in going into a situation of conflict and not understanding there is going to be a price paid."
He said many of those in the armed forces, including those who have lost loved ones in Afghanistan or Iraq, were "often proud of what their child had done and proud of the cause they fought in".
Blair, who converted to Roman Catholicism after his resignation in 2007, denied faith had played a part in his decision to send troops to conflict zones, but insisted it had given him strength.
"I think it is important that you take that decision, as it were, on the basis of what you think is right, because that is the only way to do it.
"I think people sometimes think my religious faith played a direct part in some of these decisions. It really didn't."
Anthony Howard, a commentator on British politics, told Al Jazeera that Blair was chaging his tune and trying to prepare the ground ahead of his testimony before the inquiry.
"I think he's saying this now because he knows he's got this date with the Chilcot inquiry next month and I suppose he thought it was good to prepare the ground, soften up the kind of questions he'd get by saying, 'Well, look - I would have done it anyway and that may make things easier," Howard said.
"But the difficulty with Blair is that he was absolutely explicit at the time in saying... the debate in the House of Commons, there was no doubt about it, the justification for the war was the existence of weapons of mass destruction.
"I don't think anyone realistically thinks that Tony Blair is going to end up in jail but what he has ended up with is a hefty great stain on his reputation and whether he likes it or not all those years he was prime minister, he will be remembered for not being completely candid with the British public for why he did what he did."