Under the agreement, Party of Regions head and former Ukrainian Prime Minister Viktor Yanukovych will be put forth as the coalition's candidate to head the cabinet.
"The coalition's doors will always be open, and every political force can apply for participation in the coalition," Yanukovych said today.
Collapse Of The Orange Coalition
The surprise agreement comes just hours after President Viktor Yushchenko said attempts to form a government by a coalition of liberal parties had collapsed.
Yushchenko was reacting to the July 6 election of Socialist Party leader Oleksandr Moroz as speaker of parliament.
Roman Bezsmertnyy, the faction leader of the pro-presidential Our Ukraine bloc, was equally pessimistic.
"I don't think anybody will deny that de facto the coalition ceased to exist yesterday," he told journalists in Kyiv today.
Moroz was elected thanks to support from the pro-Russian Party of Regions, invalidating a previous deal on the distribution of top positions, according to which close Yushchenko ally Petro Poroshenko was to become parliament speaker and former Prime Minister Yuliya Tymoshenko was to return as head of the cabinet.
Yushchenko said this meant the Orange coalition had basically collapsed. He said that, as a result, a new coalition might have to be created.
Parliament's Status In Question
The status of the latest coalition and of parliament itself remains unclear.
Ukraine's constitution says a coalition must be formed within 30 days of parliament's first sitting. That deadline passed almost two weeks ago, giving Yushchenko the theoretical right to dissolve the chamber.
Tymoshenko discussed this possibility with reporters in Kyiv today.
"Thirty days have passed since the parliament began its work, but there is still no coalition in the country," she said before the announcement of the leftist alliance. "So, before speaking about what this parliament is about to do, we should first wait for a legal assessment whether this parliament is legitimate and, secondly, we should wait to see whether the president is going to exercise his right to dissolve the parliament since no coalition was created within 30 days. Therefore, until the president takes a stand, the parliament does not have full legitimacy."
Yushchenko made no categorical statement today on parliament's status but stressed that the future government's legitimacy depends on observing the constitution.
"The best way to avoid future discussions about the legitimacy of the election of the head of parliament or the prime minister is to stick to the deadlines laid out in the constitution," Yushchenko said . "So, I would say in this context there is a threat of the parliament being dissolved if the forces that assumed the political responsibility to form a coalition fail to do it within these deadlines."
In the 450-seat parliament, the Party of Regions has 186 seats. The Yuliya Tymoshenko Bloc has 129 seats; Our Ukraine, 81; the Socialist Party, 33; and the Communist Party, 21.
(with additional agency reporting)
ANALYSIS: To read an RFE/RL news analysis of developments in Ukraine's parliament, click here.