Bill Clinton accepted the freedom of Belfast with a plea to its citizens to ensure the next generation is free to enjoy peace.
The former US president and senator George Mitchell, the diplomat who brokered the Good Friday Agreement, were both bestowed with the honour on the 20th anniversary of the accord.
Mr Clinton told his audience at the Ulster Hall in Belfast that he had fallen in love with the city in the 23 years since his first visit.
He joked about that high-profile occasion, in 1995, when he switched on the Christmas tree lights at City Hall little over a year after the paramilitary ceasefires, and when the peace process was still in its fledgling stages.
"I was terrified the lights would short out and the whole thing would be a metaphor for the failure of the peace process," he said.
"But in front of tens of thousands of people, the lights came on, the lights came on in Belfast and the lights stayed on.
"Through thick and thin and ups and downs and setbacks and disagreements and governments in and out of Stormont - for 20 years the lights have stayed on."
He added: "I am glad to finally have the freedom of a place which I did my small part to make free."
Mr Clinton acknowledged the difficulties presented both by Brexit and the current powersharing impasse at Stormont.
But he urged people to reflect on how far the city had come since the 1998 agreement was struck.
"I will always be grateful I came to Belfast when peace had been made but the city was still troubled," he said.
"When wise and good and decent people actually had to make a decision to do the right thing, to be the right sort of person, to give children the right sort of future.
"It was a fortune wind that blew me here.
"The least George and I can do with our freedom is to plead with you to give the same gift to generations yet to come."
Mr Mitchell described the award as an honour.
He said his time chairing the Good Friday talks changed his life.
"I have come to know and to greatly admire the people of Northern Ireland," he said.
"To receive this honour from them is very moving and gratifying to me."
The men became the 83rd and 84th recipients of the Freedom of the City of Belfast.
The event at the Ulster Hall was billed as a celebration of peace.
The ceremony was presented by local author Glenn Patterson and featured music and readings from poets including Seamus Heaney, Michael Longley, Emma Must and John Hewitt.
Lord Mayor of Belfast Nuala McAllister said: "I am absolutely delighted to be here tonight, marking such an important milestone in our history and recognising the very significant contribution made by President Clinton and senator Mitchell in peacebuilding.
"Both men played an integral role in helping to bring peace to this part of the world, and have always shown great affection towards the people of Belfast and Northern Ireland.
"Along with many other prominent peacebuilders, president Clinton
and senator Mitchell helped to bring our communities together, and paved the way for a brighter future for generations to come.
"Their place in our history is assured by receiving this honour, and both president Clinton and senator Mitchell can be very proud of what they helped us to achieve."