Germany's Social Democrats (SPD) have bought Chancellor Angela Merkel time with their vote to join her conservatives in another coalition, but she risks losing her long grip on power if she fails to balance the awkward allies' conflicting demands. In a tweet, they labeled the SPD's decision a catastrophe for Germany, promising fierce opposition to the government.
Merkel is due to be re-elected by parliament as chancellor on March 14, said Volker Kauder, parliamentary chief of her CDU party.
After September's election, in which the Social Democrats received just 20.5 per cent of the vote, then-leader Martin Schulz ruled out another grand coalition with Merkel.
But according to party treasurer Dieter Neitan, two-thirds of the 464,000 members who voted were in favour of the deal.
However, the SPD agreed to negotiate with Merkel's conservatives after talks with the pro-business Free Democrats (FDP) and the environmentalist Greens on a three-way tie-up collapsed in November.
Acting SPD leader Olaf Scholz said at the party's Berlin headquarters: "The vast majority of SPD members followed the party leadership's suggestion".
Had the long-time German leader faced a "no" result, she would have been left with only two realistic options: forming a minority government or seeking a new election.
The leadership of the SPD had initially ruled out joining Merkel in government in the wake of historically disappointing results at federal elections in September a year ago.
It also puts an end to more than four months of political uncertainty in Europe's largest economy by making Merkel the country's chancellor for the fourth term.
Both sides had been weakened as voters angry about the arrival of more than a million asylum seekers in Germany since 2015 turned to the far-right party Alternative for Germany (AfD).
But after Merkel's attempt to cobble together a government with two smaller parties failed, the SPD relented.
To stop the SPD from bolting, Merkel must deliver on those points in the coalition deal that are most dear to the Social Democrats: healthcare reform, and investment in education to meet the challenges of the digital age.
With a resumption of the "grand coalition" government now assured, the SPD's pick for finance minister will be among the most-watched decisions ahead.
Kevin Kuehnert, head of the SPD's youth wing, said he was disappointed but that the "Jusos" (youth wing) would keep up their criticism, signaling that, after bringing in a flood of new members, they would be a thorn in the leadership's side.