Thousands of people are expected to join rallies calling on President Mikheil Saakashvili to stand down.
Protesters say he provoked the war with Russia last year and that there is "no democracy" in the country.
Police used rubber bullets and tear gas to break up the last mass protests in the capital, Tblisi, in November 2007.
Mr Saakashvilli's critics say he is to blame for the country's current situation and should resign.
"I don't think that it should be a surprise that after we lost 20% of Georgian territory and have no democracy in the country, we are asking for the resignation of the president," said Nino Burjanadze.
Ms Burjanadze was formerly an ally of Mr Saakashvili but now leads the opposition Democratic Movement-United Georgia party.
The BBC's Tom Esslemont in Tblisi says opposition leaders have chosen a poignant date for the demonstrations, 20 years to the day since 20 people died when Soviet Red Army troops crushed an uprising in Tblisi.
Our correspondent says both opposition and government figures have accused one another of planning to use violence in Thursday's rallies.
Video footage was recently released by the government allegedly showing a group of opposition supporters planning a disturbance at the protests.
The government accused the men of trying to provoke the government into using force.
Interior Minister Vano Merabishvili said the government would "not intervene or impede members of the protest in expressing their will freely" but indicated that the authorities could take action if they deemed it necessary.
"My position does not give me the liberty to exclude anything, but my mood tells me there will not be violence," he told Reuters.
"There is no chance of a revolution in Georgia."
