Malawian Vice-President Joyce Banda has taken over in the southern African nation after the death of President Bingu wa Mutharika.
Ms Banda, a 61-year-old women's rights activist and education campaigner, was due to be sworn in as president later today in the National Assembly in the capital Lilongwe.
She will become southern Africa's first female head of state.
Two days after he died from a heart attack, the government officially confirmed 78-year-old Mutharika's death.
His body had been flown to a military hospital in South Africa.
The delay in the announcement had raised worries about a political crisis because Ms Banda had been expelled from Mr Mutharika's ruling DPP party in 2010 after an argument about the succession, though she retained her state position.
Dispelling fears of a power struggle, Ms Banda appeared at a news conference in Lilongwe to declare 10 days of official mourning for Mr Mutharika, who had ruled for eight years.
She ordered national flags to be flown at half-mast and the state broadcaster to play sombre music.
Malawi's constitution stipulates that the vice-president takes over if the president dies, but Mr Mutharika appeared to have been grooming his brother Peter, the foreign minister, as his de facto successor.
In a sign that Ms Banda had support across the political spectrum, opposition leaders called for her to be swiftly sworn in as head of state and some 20 members of the national governing council of Mutharika's Democratic Progressive Party (DPP) also expressed their backing for her.
She is expected to run the country until scheduled elections take place in 2014.
The streets of the main cities Lilongwe and Blantyre were calm, though police guarded strategic locations.
There appeared to be little public sorrow at Mr Mutharika's death. Many of Malawi's 13 million people had viewed him as an autocrat personally responsible for an economic crisis that stemmed ultimately from a diplomatic row with former colonial power Britain a year ago.
The presidency and cabinet issued a statement assuring citizens and the international community "that the constitution of the Republic of Malawi will be strictly adhered to in managing the transition."
Both Britain and the United States, major donors to Malawi until they froze millions of dollars in aid over rows with Mr Mutharika over his policies and actions, urged a smooth transition respecting the constitution.
Britain and others froze aid worth some 40% of government spending, fuel supplies dried up and food prices soared.
As reports of the death of the self-styled "Economist in chief" swept the capital, there were bursts of jubilation among those who accused Mutharika of turning back the clock on 18 years of democracy in the "Warm Heart of Africa".
Medical sources said Mr Mutharika's body was flown to South Africa because Malawi's energy crisis was so severe the Lilongwe state hospital would have been unable to conduct a proper autopsy or even keep his body refrigerated.
President Michael D Higgins extended his condolences to Ms Banda and the people of Malawi.
He said Ireland remains committed to working in partnership with the government and people of Malawi in a shared objective of enhancing the economic and social well-being of all its citizens.
