Mr Blair, who was Prime Minister from 1997 to 2007, chose to invade the country in 2003 alongside US President George W Bush.
The coalition aimed to find Iraq’s “weapons of mass destruction”, despite lacking support after a UN inspection team found no evidence ofWMDs before the invasion.
Mr Blair, 68, spoke to Archbishop Justin Welby for the third episode of BBC Radio 4 programme The Archbishop Interviews, which feature conversations with people who have made a significant contribution to public life.
When asked how he was able to make these big decisions, he replied: “In those circumstances, you’ve got to try and do what you think is the right thing. People would often say over Iraq or Afghanistan or other things that I took the wrong decision but you’ve got to do what you think is right.
“Whether you are right or not, that’s another matter, but in those really big decisions, you don’t know what all the different component elements are. And you’ve got to follow, in the end, your own instinct.
“And so post 9/11, I decided we had to be with America in this moment. You know, the whole issue to do with the use of chemical, biological weapons, development of nuclear weapons and so on.
“We had to take a strong, strong stand on it. Now I may have been wrong but taking those decisions, I had to do what I thought was the right thing.
“And I think that’s a very strong obligation on the Prime Minister in these situations. In the end, you just don’t know how things are going to unfold. But it’s your job to take the decision.”
While it came after 9/11 and the war in Afghanistan, the invasion of Iraq has proven to be the most controversial decision of Mr Blair’s premiership. Leader of the House of Commons Robin Cook resigned over it, and large-scale protests were held across the UK.
Archbishop Welby asked how he dealt with the widespread criticism he has faced since, something Mr Blair credited to his faith.
“Faith does help in these circumstances.
“But the other thing is that temperament is a very important thing in any position of leadership and your temperament has got to be able to withstand the criticism and also know what it means, what it doesn’t mean.”
- The Archbishop Interviews airs at 1.30pm today on BBC Radio 4.