Signing the 1998 peace deal was an act of “bravery” by all sides, Mr Clinton said ahead of his visit to Ireland later this month for the deal's 25th anniversary.
Mr Clinton added he would always be “grateful and honoured” that he played a role in bringing peace to Northern Ireland, saying “it meant more to me than I can possibly say”.
The former Democratic leader was speaking in an interview aired at Fianna Fail’s commemoration of 25 years of the Good Friday Agreement at University College Dublin on Tuesday evening.
Among those in attendance were Bertie Ahern — former Irish prime minister, Fianna Fail leader and one of the architects of the Good Friday Agreement — and Micheal Martin, Ireland’s Deputy Prime Minister and the party’s current leader.
Mr Clinton and his wife, former secretary of state Hillary Clinton, will be in Belfast in two weeks’ time for events to commemorate the landmark accord that largely ended the Troubles.
US President Joe Biden is due to visit locations north and south of the border next week for the beginning of events to celebrate the diplomatic achievement.
“The day the Good Friday Agreement was signed in 1998 was one of the happiest days of my presidency, indeed of my entire life,” Mr Clinton said during the interview.
“It was a result of years of hard work and sacrifice and bravery from all sides.
“Ultimately, the credit for the peace belongs to the people who voted for it, from all backgrounds. They made personal decisions that their future opportunities were more important than their past divisions.
“The people, especially the women’s groups, were out in front of the politicians for a long time because they wanted their children and grandchildren to have a chance to grow up outside the shadow of violence and hatred.
“An entire generation in Northern Ireland has grown up largely free from the horrors of sectarian violence.”
Mr Clinton described the move to pursue peace a quarter of a century ago as “miraculous”.
“The people of Northern Ireland did something truly miraculous 25 years ago,” he said.
“They can do something miraculous again today just by seizing this moment, sharing the memory and moving into the future together.
“I will always be grateful and honoured that I was trusted to play a role in helping to bring peace to Northern Ireland, that I had a chance to work with leaders of many parties in the North, with the leaders of government in the Republic and in the United Kingdom, and that I was able to work from the almost the very beginning of my presidency until the very end.
“It meant more to me than I can possibly say. And for the rest of my life, I will always do whatever I can to keep supporting the people and their efforts to make the most of that peace.”
In the same video interview, Mr Blair said the “strangest” moment of the Good Friday Agreement was taking a phone call from the late Queen Elizabeth II congratulating him on striking a deal.
The former Labour leader said this was significant because he had not received a mobile phone call from the late British monarch other than the one after the historic signing of the deal on April 10, 1998.
“The strangest moment for me was, we finally made the agreement, we got out, we’d announced that I hadn’t slept really for three days,” Mr Blair said.
“I had to get on a plane to go and see the Spanish prime minister, for whom I was now about three days late. And when I sat down in the plane, they brought to me a mobile phone and it was the queen on the line.
“And it was only when she was congratulating me and all the other people that had been engaged in the creation of the agreement that I remember thinking: ‘Wow, actually this really is big because I’ve never taken — before or since — I never took a mobile phone call from the queen’.”