"If we do not act immediately, then the consequences will be great, with 2010 a difficult year ahead for the economy."
The move is risky as his scandal-plagued conservative New Democracy government trails the main opposition socialist Pasok party by about six percentage points in opinion polls.
The conservatives, who currently have a one-seat majority in parliament, have suffered months of scandals and their popularity has sunk lower after criticism of their response to recent wildfires which hit the outskirts of the Greek capital last month.
The socialists, themselves burdened with scandals during decades in government, have long pressed for an early vote and would have been in position to force one in March.
Pasok advocates a "green growth" economic model.
They have said that if the election fails to win an outright majority, they will call for a second vote under a revised electoral law that makes it easier to form a government with fewer votes.
Seen by investors as the euro zone's riskiest bet, Greece is struggling to cope with the global slowdown that is threatening to push its economy into recession this year while its national debt is ballooning.