In his inaugural address, the new president set out a programme of dramatic change that promised a stark reversal of many of Mugabe’s signature policies.
He pledged that his government would compensate white farmers whose land was seized by Mugabe, protect international investments in the country, and re-engage with foreign powers.
Elections scheduled for 2018 would go ahead as planned, he said.
“I humbly appeal to all of us that we let bygones be bygones,” he said at the ceremony in the 60,000-seat national stadium, which was packed to capacity.
Two days later, Mnangagwa fled the country, only returning on Wednesday when he said Zimbabwe was entering an era of “full democracy”.
But critics have warned Mnangagwa — whose ruthlessness won him the nickname “The Crocodile” and who has been accused of overseeing violence and ethnic massacres — could prove just as authoritarian as his mentor.
Friday’s 21-gun salute marked Mnangagwa’s transformation from a sacked enemy of the state to president of a nation of 16 million people.
“We thank you, our soldier,” read one banner at the stadium.
“The people have spoken,” said another.
“Mnangagwa came at the right time when the economy was showing signs of going back to 2008 when… people were starving,” said Nozithelo Mhlanga, a 27-year-old accountant.
“Mugabe has left no legacy at all except that of ruin, poverty and corruption.
Mugabe, who is in increasingly frail health, had been positioning his wife Grace as his successor but the army chiefs stepped in to halt the plan.
Police commissioner Augustine Chihuri, seen as a Grace supporter, was loudly booed at the swearing in.
Mugabe did not attend.
Mnangagwa promised the Mugabes “maximum security and welfare” in talks on Thursday.
Opposition leader Morgan Tsvangirai, who heads the Movement for Democratic Change received rapturous applause as he arrived at the packed stadium.
Also at the ceremony were Zambian President Edgar Lungu, Botswana’s President Ian Khama and Zambian independence leader Kenneth Kaunda — known as “Africa’s Gandhi” — all of whom were cheered.
Jacob Zuma, president of regional heavyweight South Africa, did not attend as he was hosting a visit by Angola’s new head of state.
“We wish to emphasise the need for the maintenance of peace and stability,” said Zuma in a statement.
Robert Besseling, of the London-based EXX Africa risk consultancy, wrote in a research note that ensuring economic stability would be paramount.
“Mnangagwa’s administration will also reach out to foreign banks to obtain fresh financial support facilities,” he wrote.
Mugabe had ruled Zimbabwe since its independence in 1980, exercising almost total authority to crush any sign of dissent.
The majority of Zimbabweans have only known life under Mugabe whose reign was characterised by brutality, rigged elections and international isolation.
Until his rule ended on Tuesday with a resignation letter read out in parliament where MPs had gathered to impeach him, he was the world’s oldest head of state.
Mugabe was last seen in public on Friday. Neither he nor his wife Grace has been seen since.
In the week before Mugabe resigned, military vehicles rolled onto the streets of Harare and tens of thousands of Zimbabweans demonstrated against the veteran leader.
Zimbabwe’s once-promising economy collapsed under Mugabe, and many hope Mnangagwa will push through investor-friendly reforms.
Unemployment is over 90 percent, and in his first speech after being announced as the next president he promised “jobs, jobs, jobs!”