Party leader Alexis Tsipras has pledged to renegotiate Greece’s E240bn (£179bn) international bailout deal.
He promises to reverse many of the reforms that creditors demanded in exchange for keeping Greece financially afloat since 2010, potentially placing the country on collision course with Angela Merkel’s Germany, Europe’s largest economy.
The euro fell in early trading in markets in Australasia as traders reacted to exit polls showing a convincing lead for Syriza, with the currency nearing the 11-year low against the US dollar it hit last week.
The currency lost nearly half a cent to around $1.1167 after hitting 1.1115 last week, its lowest since September 2003.
The result means there will be watchful eyes on the currency when markets in Europe open tomorrow morning.
Greek election officials said the Syriza party had won the national elections but it was too soon to say whether it has enough support to form an outright majority.
The Interior Ministry said that its projections, based on early returns, showed Syriza one short of a majority, gaining 150 of the 300 seats in parliament. Mr Tsipras is hoping for a big enough margin of victory over Prime Minister Antonis Samaras’s incumbent party to be able to govern alone.
Official results from 17.6 per cent of polling stations counted showed Syriza with 35 per cent and Mr Samaras’s New Democracy (ND) with 29.3 per cent. An exit poll on state-run Nerit TV projected Syriza as winning with between 36 per cent and 38 per cent, compared to ND with 26 to 28 per cent.
Mr Tsipras has vowed to reverse many of the austerity measures imposed since 2010, including cuts in pensions and the minimum wage, some privatisations and public sector job losses.
Mr Samaras tonight conceded defeat to the radical left-wing Syriza party, saying he is delivering a country that has put the worst of its financial crisis behind it.