The agreement between Merkel and Sarkozy was struck at a surprise meeting in Berlin on Wednesday night during discussions lasting more than six hours in the chancellery after several weeks of wrangling between euro zone partners over the terms of a new bailout package for Greece.
They were unexpectedly joined for more than one hour by European Central Bank President Jean-Claude Trichet, a government spokesman said.
Their decisions were taken in consultation with Herman Van Rompuy, the president of the European Council, who hosts the summit.
The meeting between Merkel and Sarkozy was hurriedly arranged during a telephone conversation on Tuesday and the leaders of Europe's two largest economies apparently wanted to demonstrate once again that they hold the key to an agreement on a major issue affecting the future of Europe.
The euro zone leaders have been under pressure in the past weeks to reach a speedy agreement on a second rescue package of about 120 billion euros in order to send a strong message to increasingly nervous financial markets that they will act decisively to deal with the Greek crisis and safeguard the stability of their common currency.
A second rescue package over a year after Greece received 110 billion euros became necessary to avert the Greek crisis spilling over to larger euro zone economies such as Spain and Italy.