Mr. Merz needed two rounds of voting to become chancellor after a surprising defeat in Parliament hours earlier that threatened to hobble his new government.

It was the first time in Germany’s postwar history that a chancellor-designate has failed to win an absolute majority.

In a historic first, conservative leader Friedrich Merz ’s bid to become Germany’s 10th chancellor since World War II failed by six votes in parliament on Tuesday, a stunning defeat as he had been widely expected to win smoothly.