Antonis Samaras, head of Greece's conservative New Democracy party, has been sworn in as the country's new prime minister, following his victory in Sunday's general election.
New Democracy, the socialist party Pasok and the smaller Democratic Left came to an agreement on Wednesday to form a coalition government.
All three parties support Greece's loan commitments, unlike the second-placed Syriza, but have pledged to rewrite the conditions of the bailout.
Samaras took the oath at a Greek Orthodox ceremony in Athens. "With the help of God we will do whatever passes from our hands to get out of this crisis," he said in his first statement in office.
Evangelos Venizelos, the Pasok leader, has said the next two weeks will be critical for the debt-stricken country.
In a televised address Venizelos said the government's top priority would be the formation of "a national team" to renegotiate the €130bn bailout agreement Athens had signed with its creditors at the EU and IMF.
"Our first test will be the EU summit on 28 June where our battle to revise the terms of the loan agreement with our creditors will begin," he said.
Referring to the far-left party's refusal to take part, given that it would be the country's main opposition party, he added: "It is a pity that Syriza has refused to participate in this team."
Venizelos, who negotiated the accord when he was finance minister in an interim government headed by the technocrat Lucas Papademos, announced that like the Democratic Left, Pasok MPs would support the coalition but not participate in the cabinet.
Announcements on the cabinet are expected on Wednesday evening.
Aides said Greece's new coalition would demonstrate that stability was returning to the country.
"We wanted to send a message to markets and foreign governments that we have a leader and tomorrow we will have a government," one aide said.
"We didn't want to protract the sense of instability and insecurity. We wanted to show that things are rolling, they are being resolved, that step by step, day by day, stability is returning to Greece."
The three parties have a combined 179 seats in Greece's 300-seat parliament.
Pasok and New Democracy alternated as Greece's ruling parties since the end of military rule in 1974 to the short-lived national unity government formed under Papademos at the end of last year.