Syriza`s leader, Alexis Tsipras, called the snap poll after securing a multi-billion euro international bailout.
Whoever is elected will have to oversee austerity measures demanded by Greece`s creditors as part of the deal.
Syriza supporters` gathered in central Athens for the party`s final rally on Friday, in what Mr Tsipas said sent "a message of determination and victory".
"On Sunday, we`re facing a crucial referendum - to put an end to old political system, protecting oligarchs and corruption," he tweeted.
At the final New Democracy rally, its leader Vangelis Meimarakis attacked Syriza`s "false promises" in the run-up to the last election, when it pledged to end austerity.
"It`s high time we did away with incompetence. The Syriza experiment ends on Sunday," he said.
At a debate earlier in the week, Mr Meimarakis proposed forming a grand coalition with Syriza but Mr Tsipras rejected it as "unnatural".
Most of the parties support the bailout. But one of those that does not - the far-right Golden Dawn - is predicted to come third.
Analysts say the migrant crisis on Greece`s doorstep may bolster support for Golden Dawn, which is vehemently opposed to immigration.
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