The Socialist party has said it will stop blocking the conservative Popular Party from forming a minority government in Spain.
It should end the country's nearly 10-month political impasse.
Members of the Socialists' federal committee said they would abstain from voting against acting Prime Minister Mariano Rajoy during a confidence vote in Parliament.
The committee voted 139 to 96 in favor of the abstention, a decision that should prevent a third election.
Two inconclusive elections since last December left Mr Rajoy in charge of a caretaker government. His Popular Party won both elections, but not enough seats to form a majority in Parliament.
Spain has been led for decades by either the conservatives or the Socialists and has never had a coalition government.