During the most difficult periods in crucial talks between Sinn Féin and the DUP, the former Prime Minister felt it would be "impossible" to achieve peace.
"There were times when I though it was going to be impossible, yes, I did actually," he told UTV's Political Editor Ken Reid on Saturday.
But Mr Blair added that once he had committed to the process there was no turning back.
"I felt that once I'd really committed that was it, I was going to carry on," he continued.
In his eagerly-awaited memoirs, which were published last week, the former Prime Minister said he sometimes stretched the truth "past breaking point", when talks to restore the power-sharing institutions were deadlocked between Sinn Féin and the DUP.
He said he took "horrendous chances" over what he told each party the others had agreed, adding that it was necessary in order to keep the peace talks between the two parties alive.
"Look, I am just trying to be open about this and by the way I don't mean that you always do it or that you actually deceive people", he told Ken Reid.
"I was really talking about in relation to a very difficult passage between Gerry Adams and Ian Paisley where it wasn't so much that I was sort of misleading either but I was not passing on the full extent of the gulf from one to the other because I actually thought if I did that we were going to tip the thing over the edge and we were going to lose it."
Around 8,000 words of Mr Blair's autobiography 'A Journey' are devoted to Northern Ireland.
In the book he confirms he held one-to-one discussions with Dr Ian Paisley on spiritual matters in the period leading up the 2007 power-sharing agreement.
He says his scepticism about Dr Ian Paisley changed into confidence that he could deliver.
Asked if he felt the political process was too strong now to be turned around, Mr Blair told UTV:
"I think so. It's hard for me to really judge without going back in there and really spending time there, but I think so.
"There will be elements that want to disrupt through use of terrorism and so on, but I don't think they have a foothold anywhere in mainstream opinion.
"If we're careful and prudent and vigilant, then we will make it hold."
Mr Blair says he is very proud of his achievements in Northern Ireland.
"I see it as a big part of what we did in government. It was a big part. It is something I am very proud of and it is something I hope will stand the test of time," he told UTV.
Mr Blair spoke to Ken Reid before a book signing session at a Dublin store was disrupted by demonstrators.
Shoes and eggs were pelted at the former Prime Minister as he arrived at the O'Connell street store on Saturday.
Mr Blair has now cancelled another high-profile signing session of his new memoir in central London amid concerns over planned protests.
The former prime minister was due to attend the flagship Waterstone's store in Piccadilly on Wednesday - where anti-war campaigners had promised a hostile reception.
But he said he did not want to subject the public to the "inevitable hassle" protests would cause or use up police resources keeping order at the event.
Announcing the decision in a statement, Mr Blair said he would provide signed copies to the store for those who had planned to attend.
"However, I have decided not to go ahead with the signing as I don't want the public to be inconvenienced by the inevitable hassle caused by protesters.
"I know the Metropolitan Police would, as ever, have done a superb job in managing any disruption but I do not wish to impose an extra strain on police resources, simply for a book signing.
"I'm really sorry for those - as ever the majority - who would have come to have their books signed by me in person. I hope they understand."