Mr Karamanlis said Greece needed leadership in difficult times
Greek Prime Minister Costas Karamanlis has confirmed that a snap general election will be held on 4 October.
He asked President Karolos Papoulias to dissolve parliament as of Monday, after announcing the election on Wednesday.
Mr Karamanlis called for a new mandate to tackle the economy, but he has been hurt by financial scandals and the effects of recent wildfires.
His conservative party has a majority of just one seat in parliament and has been trailing the opposition in polls.
"I am seeking a fresh political mandate," Mr Karamanlis said on TV on Wednesday.
"My act is an act of responsibility, I didn't have the right to let the country be dragged for months in a pre-election atmosphere."
Former Foreign Minister George Papandreou, leader of the socialist opposition, is expected to respond at an event in Athens to mark his party's 35th anniversary later on Thursday.
Mr Karamanlis said in his address on Wednesday: "We have to clarify the political landscape and proceed with a series of essential measures to emerge from the downturn.
"The year 2010 will be a difficult and decisive one, and so the Greek people must choose a government that can lead the country out of this crisis."
There has been social unrest since police shot a teenager last December
The conservative New Democracy party trailed the Socialists by six points in two recent opinion polls and the snap election had been opposed by some conservative MPs.
A senior member of the party, Yiannis Manolis, resigned his seat on Monday, saying he was disappointed with the government's performance, but his seat would have been taken by another conservative without the need for a new election.
The government has been hit by a series of corruption scandals.
Aristotle Pavlides, a former minister, was alleged to have solicited bribes in return for granting shipping contracts, although he denied any wrongdoing.
Last October two ministers resigned after it emerged that state land was given to a monastery on Mount Athos, in return for much less valuable land.
Previously, a labour minister quit after employing uninsured immigrants, and his predecessor was forced out amid a bond-trading scandal.
Greece has also been dogged by social unrest since police shot a teenager dead last December.
The death sparked the country's worst riots in decades, leading to clashes between police and protesters in the weeks that followed.
Shortly before Mr Karamanlis announced the election on Wednesday, a bomb went off outside the Athens stock exchange, slightly injuring a female passer-by and damaging the building.
The BBC's Malcolm Brabant in Athens says the blasts may be the work of the extremist group, Revolutionary Struggle.