Alexis Tsipras has won a resounding victory in the weekend's Greek general election.
Tsipras' far-left Syriza party won comfortably with 35.5 per cent of the vote, giving it 145 seats in the 300 member Parliament, just short of a majority.
The election result met with mixed reaction from EU policymakers in Brussels.
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Manfred Weber, chair of the European Parliament's centre right EPP group and a strong critic of Tsipras, called on the returning Greek Prime Minister to "cooperate with the other constructive and democratic parties in Greece," highlighting the need for "a stable government that accepts the EU rules of the game."
He went on to add that New Democracy, the centre-right party that Tsipras beat, "have the skill and experience to serve the interests of all Greeks," having proven it is "the most trustworthy political force in Greece."
Martin Schulz, the European Parliament's President, also called on the need for stable government while offering his congratulations to Tsipras. Schulz tweeted, "I've just congratulated Tsipras. Now a solid government ready to deliver is needed quickly."
However, like Weber, the centre left Schulz was critical of Tsipras, calling into question his decision to align with the extreme right Independent Greeks party.
Schulz told a French radio station, "I called him [Tsipras] a second time to ask him why he was continuing a coalition with this strange, far-right party. He pretty much didn't answer. He told me things that seemed convincing, but which ultimately in my eyes are a little bizarre."
Nigel Farage, the anti-EU UKIP party leader and chair of parliament's EFDD grouping, called into question the validity of the election itself, highlighting the low voter turnout with only 55 per cent of the population voting.
Farage tweeted, "surge in Greece of those who didn't vote at all. Record low turnout. Democracy crushed by EU membership."
Other senior European figures took a more conciliatory approach with European Council President Donald Tusk highlighting the important role Tsipras will play in implementing the country's recently agreed bailout programme and for the need for the EU to show solidarity with Greece.
Tusk said, "Your dedication and leadership in implementing the economic adjustment programme is crucial to making a difference in the recovery of the Greek economy."
He added, "many of the biggest challenges facing the European Union are the same as those facing Greece as a country."
Mina Andreeva, deputy spokeswoman for European Commission President Jean-Claude Juncker, also acknowledged Tsipras's win and called on him to implement the economic reforms the country signed up to in the bailout package.
Andreeva tweeted, "Juncker congratulates Tsipras for his election victory. New gov. will now have mandate to carry out reforms it signed up to."
Gianni Pittella, the leader of Parliament's S&D group, called the result a "victory for democracy and a clear defeat for the right," and called for "the EU and its member states to act together and co-operate with the new government."
Tsipras will need all the help he can get. His first task will be to put into action the tough austerity measures agreed in the €86bn bailout package signed in July.