Antonis Samaras, the leader of the New Democracy party, which won Sunday’s election, has been sworn in as the country’s new prime minister.
The ceremony came shortly after he agreed a coalition government with the Socialists (Pasok) and the smaller leftist party, the Democratic Left.
Mr Samaras was sworn in by the archbishop of Greece in Athens.
He vowed his government would do whatever it could to tackle an economic crisis that has shaken the eurozone.
“I am asking the Greek people for patriotism and strong national unity and trust, [so] that with the help of God, we’ll do whatever we can for the people to come out of this crisis,” he said in his first public words following the ceremony.
The 61-year-old said he would demand “hard work” from the new government “so that it will be able to give hope to our people”.
The coalition deal follows weeks of uncertainty, after parties failed to agree a government on the results of an election on 6 May.
But the new coalition is expected to come under immediate pressure from a Greek public weary of five years of recession and increasingly resistant to the tough terms of Greece’s huge bailout from the EU and International Monetary Fund (IMF).
Syriza – the leftist party that came second in Sunday’s poll and strongly opposes the tough austerity measures required under the bailout deal – will be a defiant voice of opposition, correspondents say.
‘Burden of responsibility’
Mr Samaras took the oath of office at a brief ceremony at the presidential palace in Athens, presided over by chanting Orthodox Greek clergy.
The three coalition party leaders are due to meet outgoing Finance Minister Giorgos Zanias and the man tipped to be his successor, National Bank chairman Vassilis Rapanos, on Wednesday evening.
More detail on the make-up of the cabinet is also expected to emerge before Thursday, when Mr Zanias will represent the new government at a meeting of eurozone finance ministers in Luxembourg.
Earlier, announcing the coalition deal, Pasok leader Evangelos Venizelos said the three parties in the new coalition had “taken on the burden of responsibility to renegotiate the bailout agreement and [the job] of exiting Greece from the crisis”.
Democratic Left leader Fotis Kouvelis said he expected the cabinet to “release the country from the painful terms” of the bailout, reported AFP news agency.
The BBC’s Andrew Walker in Brussels says European leaders will be relieved that there is now a Greek government to negotiate with, but concern about what they will be asking for.
European leaders have indicated that there is limited room for manoeuvre on the bailout.
Greece has seen many street demonstrations – sometimes violent – by people angered by the job losses, pay cuts and reduced welfare resulting from the bailout.
The country got an initial EU-IMF package worth 110bn euros (£89bn; $138bn) in 2010, then a follow-up this year worth 130bn euros.
It has also had 107bn euros (£86bn; $135bn) of debt, held by private investors, written off.
New Democracy won 129 seats in Greece’s 300-seat parliament on Sunday, followed by Syriza with 71, Pasok with 33 and the Democratic Left with 17.
Between them, New Democracy, Pasok and Democratic Left would have a majority of 29.