The opposition had said before polls closed that they would rally 100,000 people in the centre of Tbilisi to protest after the election.
The first official results are not expected until later in the night and if the exit poll is accurate, then Saakashvili's party would win more than half the 150 seats in parliament.
The exit poll put the Christian Democratic Movement third with about eight to nine per cent and the Labour party fourth with about five to six per cent.
After voting, Saakashvili said: "Georgia is really a role model for many countries in this region and we intend to stay this way despite all the external pressures we are coming under."
The elections are being seen as a test of the country's democratic process as it seeks to join Nato and gain Western support in an increasingly bitter row with Russia.
Moscow is backing the separatist Georgian region of Abkhazia and has sent peacekeeping troops to the area.
Before the vote on Wednesday, Saakashvili made an appeal for national unity, saying that Russia would take advantage of any unrest.
"We have to realise how important [the] elections are," he said.
"Our enemy wants tomorrow's elections to turn into turmoil and internal confrontation.
"Our enemy is trying to weaken us and we must respond by consolidating our main values - liberty and democracy."
The poll came against a background of violence on Wednesday with incidents in and around Abkhazia.
A bus carrying voters was shot at, leaving several people injured and causing a shootout that lasted for 20 minutes.
The government blamed the attack on Abkhaz separatists.
Diplomats have cautioned that the vote will have to have been conducted fairly if Georgia is to obtain Western support in the row over Abkhazia and South Ossetia - the other separatist region backed by Russia.
Georgia's image as a "rare beacon of democracy" in the former Soviet Union was tarred in November when Saakashvili sent in riot troops to crush protests.
Opponents said he rigged a January presidential poll, a charge he denies.
The Organisation for Security and Co-operation in Europe (OSCE), the main Western election monitoring body, has sent 550 observers to monitor the vote and is to deliver a verdict on its conduct on Thursday.
Saakashvili became the "darling of the West" after he gained power in 2003, promising market reforms, a greater adherence to democracy and re-orienting the country towards the European mainstream.
But the opposition says that Saakashvili's rhetoric about democracy masks his intolerance of dissent.
Nato, which has told Georgia that it can join the alliance in the future, has said it will also be watching to ensure the election is fair.