The United Nations Migration Agency confirmed his death writing online: “It is with immense sadness that the Annan family and the Kofi Annan Foundation announce that Kofi Annan, former Secretary General of the United Nations and Nobel Peace Laureate, passed away peacefully on Saturday 18th August after a short illness”
Mr Annan, who died in a hospital in Switzerland, was one of the world’s most celebrated diplomats.
Current UN Secretary-General Antonio Guterres described his predecessor as “a guiding force for good”.
Mr Annan spent almost his entire career as an administrator in the UN and served two terms as secretary-general from January 1997 to December 2006.
He was awarded the Nobel Peace Prize in 2001.
His death was first announced by the UN migration body, which tweeted: “Today we mourn the loss of a great man, a leader, and a visionary.”
It went on: “A life well lived. A life worth celebrating.”
Speaking moments after the announcement, UN special envoy Peter Thompson told Sky News: “He was one of the great diplomats of our time.”
Remembering Mr Annan’s Nobel prize, Mr Thompson said: “He was one of our greats.”
And he added: “As a Ghanaian – a son of Africa – it is a wonderful thing to see in one of the top world positions… he carried on the legacy of Nelson Mandela… and he definitely has a place in history in that regard.”
The Kofi Annan Foundation said in a statement that wife Nane and their children Ama, Kojo and Nina were by his side during his last days.