Tony Blair has spoken to the BBC about his first spiritual experience, which occurred when he was a child.
The ex-prime minister said that praying for his atheist father when he became seriously ill had "a tremendous impact" on him.
Elsewhere in the interview with Joan Bakewell, Mr Blair defended the decision to invade Iraq, and insisted that faith schools are not divisive.
He also said that he reads the Koran nearly every day.
Blair converted to Catholicism after leaving office
In the interview, to be broadcast in the "Belief" programme on BBC Radio 3, Mr Blair reveals that when he was 10 years old his father had a stroke.
Despite the seriousness of that illness, his mother wanted her son's life to carry on as normal, so he continued to go to school, where he ended up praying for his father with the headmaster.
"I said to him 'Before we pray, I should tell you that my father, he doesn't believe in God.
"And I always remember the headmaster saying to me 'Well, that doesn't matter because God believes in him'".
He described the experience as having a "tremendous impact" on him.
Mr Blair also spoke about the role of faith schools in the state sector.
During his time as prime minister, the academy schools programme was launched.
He believes that expanding faith school provision helped to foster inter-faith relations, adding that a question of equality was involved.
I certainly don't believe that there is a Christian conviction that is superior one way or another on what the right thing to do is
"You can't say to Christians and to Jews that you can have a faith school but Muslims can't".
"I think they can help give a sense of values, they can ground a child, they can instil a certain amount of discipline, in the right way, in a child's mind, provided that they approach religion in a non-sectarian way."
Blair's family on his mother's side were Irish Protestants, which he suggested gave him a personal connection with Ireland.
His grandfather was a grand master of an Orange Order lodge, a fact that he jokingly suggested may have helped in the Northern Ireland peace process.
"Every so often some guy who would say he was a cousin of mine would sort of wander up and say 'You don't know me, but we're related'".
On the issue of Iraq, Mr Blair insisted that Britain went to war for the right reasons, and that a previous policy of appeasement towards Saddam Hussein in the 1980s had led to the Iran-Iraq war and a million casualties.
He denied thinking that his Christian beliefs meant that he considered his decisions at the time of the invasion to be automatically the right thing to do.
"I certainly don't believe that there is a Christian conviction that is superior one way or another on what the right thing to do is."
He said the decision to invade Iraq was something he reflected on every day.
Mr Blair added that his religious beliefs help him - accepting that there is a God can be frightening but it is also a source of comfort.
He also spoke about the motivations of insurgents in Iraq and Afghanistan, and rejected arguments that British foreign policy has radicalised Muslims.
"I think actually these acts of terrorism are utterly evil, yes. And when you think of the numbers of wholly innocent people that have died... I say the responsibility lies with the people doing the terrorism, 'cos there's no reason for them to do the terrorism."
Belief is broadcast on BBC Radio 3 on 10 Friday April at 2300 BST.
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