He was aged 95.
Mugabe died in Singapore, where he had been receiving medical care for months as his health deteriorated.
“It is with the utmost sadness that I announce the passing on of Zimbabwe’s founding father and former President, Cde Robert Mugabe,” a post on Mnangagwa’s official presidential Twitter account early Friday said.
Mnangagwa called Mugabe “an icon of liberation, a pan-Africanist who dedicated his life to the emancipation and empowerment of his people. His contribution to the history of our nation and continent will never be forgotten. May his soul rest in eternal peace.”
In November, Mnangagwa said Mugabe was no longer able to walk when he had been admitted to a hospital in Singapore, without saying what treatment Mugabe had been undergoing.
Officials often said he was being treated for a cataract, denying frequent private media reports that he had prostate cancer.
Monica mutsvangwa, the minister of information, confirmed the death, saying: “Yes it is really saddening. Some of us were like his children to him. We can never write our history without mentioning him.”
The former president, whose long rule in Zimbabwe descended into tyranny, corruption and incompetence, was in power for close to four decades before being ousted in a military takeover in November 2017.
He was initially loved and regarded as an African liberation hero and champion of racial reconciliation when he came to power in a nation divided by nearly a century of white colonial rule.