Greece's right-wing Independent Greeks party said on Sunday it would ally with election winners SYRIZA to form a coalition government.
"From tomorrow morning, with Alexis Tspiras as Prime Minister we will form a government," Independent Greeks president Panos Kammenos told reporters.
SYRIZA was emerging as the clear winner in Sunday's poll, with 35.5 percent based on more than half of votes counted. That would give it 145 seats in the 300-strong parliament.
Kammenos's party was polling about 3.7 percent, with an estimated 10 seats.