Democratic Left, the leftist part formed in June 2010 by MPs who broke away from the Coalition of the Radical Left (SYRIZA), has 10 MPs, enough to form a parliamentary group.
Party leader Fotis Kouvelis is expected to send a letter to parliamentary speaker Fiilippos Petsalnikos on Monday to announce that the parliamentary group will be formed.
This will give Democratic Left extra privileges in Parliament, such as the party having its own office in the House and its MPs being able to table legislative proposals.
Democratic Left now has one more MP than SYRIZA, which has nine. Four SYRIZA MPs left the party in June 2010 to form Democratic Left but their ranks swelled by the arrival this month of six MPs who were ousted from their party for voting against the terms of the EU-IMF loan agreement.
Opinion polls over the last few months have shown support for Democratic Left rising, with some surveys placing it as the second-most popular party.