Mr Papademos, an economist, was made prime minister last November to help steer Greece through its debt crisis.
He told a cabinet meeting that the government had left behind "an important legacy" and would continue its work during the election campaign.
After asking President Karolos Papoulias to dissolve parliament, he will then speak on national TV.
The election will be Greece's first since the start of the debt crisis that has led to drastic spending cuts and violent protests.
Opinion polls suggest parties opposed to austerity could make big gains.
The BBC's Mark Lowen in Athens says the 6 May date comes after months of speculation and raises the prospect of a short and highly-charged campaign.
Mr Papademos, 64, told his ministerial colleagues that in the five months since their interim government had been formed they had shown that "we can co-operate, combine viewpoints when necessary and put our differences aside, making decisions for the good of the country".