Saakashvili conceded defeat in the parliamentary elections and said that his party would be in opposition in the new Parliament.
With 97% of votes counted, Ivanishvili’s Georgian Dream led with 55% of votes while Saakashvili’s United National Movement (UNM) party trailed at 40%. Georgian Dream will have more than half of the 150 seats in Parliament.
Speaking at a press conference, Ivanishvili called on Saakashvili to resign and for snap elections to be held to choose a new president. Saakshvili's mandate expires in the autumn of 2013 and according to the constitution, he cannot be elected for a third term. He has been in office since 2004.
The president currently has more powers than the prime minister, but constitutional changes are underway to rebalance them in favour of the parliament and the executive.
Giga Bokeria, Saakashvili’s national security adviser, spoke on television to make it clear that there would be no snap presidential elections. “If someone is interested in provoking a crisis, this is a very dangerous choice,” he said.
Ivanishvili, who made his money in Russia and had been accused during the campaign of being a Kremlin stooge, also said yesterday he would not change Georgia's Western orientation and would continue to seek further integration with NATO and the EU. Ivanishvili, who was stripped of his Georgian nationality by the Saakashvili regime, has French citizenship.
The tycoon also declared his intention to normalise ties with Russia. Tbilisi has no diplomatic relations with Moscow since the brief August 2008 war, following which Georgia lost control of Abkhazia and South Ossetia. The war was largely provoked by Saakashvili (see background).
In an interview with the Euronews TV channel, Ivanishvili said that he sees the three Baltic republics as a model for Georgia. Estonia, Latvia and Lithuania are also former Soviet republics, but are now members of NATO and of the EU.
Ivanishvili said no ministers in the current government would keep their jobs, and added that while there would be no witch-hunt, some officials who had committed criminal acts would be brought to justice.
Dmitry Medvedev, who was president and commander-in-chief when Georgia fought its disastrous war with Russia in 2008, expressed hopes that the result would improve the relationship between the two countries.
"We can only welcome this as it probably means that more constructive and responsible forces will appear in parliament," Russian news agencies quoted Medvedev, now prime minister, as saying.
The EU acknowledged the election results and said its commitment to Georgia remained unchanged. "We look forward to further continued close cooperation," said Maja Kocijancic, a spokeswoman for High Representative Catherine Ashton, as quoted by AFP.
"We remain committed to both political association as well as economic integration," she added.
Saying the election campaign was "hard-fought and intense", the spokeswoman added that the EU congratulated both sides “on the inclusive and constructive nature of their first reactions".
The 1,600 international election monitors in the country announced that in spite of some irregularities and stilted media coverage, the vote had been largely free and fair.