Making their announcement late on Wednesday night, SPD officials in the state said they had voted 18 to six to take up coalition negotiations with the CDU instead of pursuing a three-party government with the hard-line socialists from The Left and the Greens.
“We're convinced such a coalition will be more stable,” said Chrstoph Matschie, the head of the SPD's state chapter in Thuringia.
After Chancellor Angela Merkel's Christian Democrats won last Sunday's federal election with the pro-business Free Democrats, there had been speculation the Social Democrats would not enter so-called grand coalitions with the CDU in Thuringia and Saarland, which both held state polls on August 30.
The decision means Christine Lieberknecht from the CDU will likely become Thuringia's state premier.
“I'm very pleased about this decision,” she said. “We will quickly move to take up coalition negotiations with the SPD and forge an effective government for Thuringia.”
The battle for the premier post had been the biggest stumbling block to a left-wing coalition in Thuringia, as Matschie had refused to accept anyone from The Left even though the socialists won more votes than the SPD.
Knut Korschewsky, The Left's party boss in the state, called the SPD decision “clearly betraying” the will of voters in the state and that the Social Democrats had let themselves be “bought” by the promises of the conservatives.