With almost all ballots counted, New Democracy had won nearly 30% of the vote, the Interior Ministry said, giving the party 129 seats in the country's 300-seat Parliament.
Syriza, which campaigned against the terms of the bailout, got 71 seats.
Pasok, which long dominated Greek politics, won 33. Four smaller parties took fewer than two dozen seats each.
Alexis Tsipras, the fiery leader of the leftist Syriza party, met with Samaras but said Monday he would not back a coalition.
"History and the people will judge them by their results," Tsipras said of the parties backing some kind of bailout deal with the creditors who are keeping Greece afloat. "Shortly we will be vindicated."
He said his party's nearly 27% showing had forced Greek leaders to realize the bailout is "nonviable," and said Syriza would press as a member of the opposition for the bailout to be scrapped in its entirety.
The vote was widely seen as a referendum on whether Greece should remain tied to the euro, the currency used by 325 million people across 17 countries in Europe. The possibility of a "no" vote roiled world markets, with some analysts warning that the collapse of the euro would cost $1 trillion.
International bailouts have kept Greece from defaulting in the face of an ongoing recession and low tax revenue, but lenders have demanded hugely unpopular government budget cuts in exchange.
Some observers had predicted that efforts to renegotiate the bailout could lead to a run on Greek banks and deeper misery.
The country must identify additional budget cuts by the end of June to be considered compliant with the terms of its bailout. After five years of recession, unemployment is running at about 22%, taxes are going up and many of those with jobs are suffering cuts to wages.
German Chancellor Angela Merkel, Europe's powerful advocate for balancing budgets to build a strong basis for economic growth, had urged Greeks not to walk away from the international loan deals.
"We will stick to the agreements. That is the basis on which Europe will prosper," she said Saturday.