One of the most powerful figures in German politics resigned abruptly under pressure on Saturday, because of his newborn baby.

It was a dizzying end to an overnight scandal that had engulfed the start of the German government’s normally sleepy summer season — and which reignited a smoldering national debate over surrogate parenthood.

At the center of the storm was Jens Spahn, a key ally and sometimes rival of Chancellor Friedrich Merz, both members of the center-right Christian Democrats. Mr. Spahn, 46, the leader of the party in Parliament, is a former federal health minister who has forged deep ties to the Republican Party under President Trump, including attending the 2024 Republican National Convention.

As health minister under Chancellor Angela Merkel, he had survived one public controversy during the coronavirus pandemic, over his ministry’s order of a half-million protective masks from a company that employed his husband.

He did not survive this one. Mr. Spahn stirred national outcry this week when he announced, on social media and in the tabloid paper Bild, that he and his husband, Daniel Funke, had become fathers to a son via a surrogate in the United States.

Surrogacy is prohibited under German law. Mr. Spahn had defended that ban throughout his career, including as health minister.

The birth announcement brought immediate cries of hypocrisy from across the political spectrum, including in Mr. Spahn’s own party. Some regional leaders of the Christian Democrats demanded his ouster. News outlets teemed with outrage.

“Is Spahn, the highest representative of the government coalition in the Bundestag, above the law?” asked the Frankfurter Allgemeine Zeitung, a top national newspaper.

Mr. Spahn defended himself, essentially, on a technicality: German law does not punish parents who use surrogates abroad. He told a podcast interviewer he had struggled with the decision but chose to prioritize his family.

On Saturday, Mr. Merz called on Mr. Spahn to step down as parliamentary leader, German media outlets reported. Almost immediately, Mr. Spahn complied, though it appeared Saturday he was leaving only his leadership post, and not his seat in Parliament.

Mr. Merz praised the decision, writing on the social media platform X that it was “right and was inevitable.”

Analysts said Mr. Spahn had broken the trust of German voters and risked dragging down Mr. Merz’s already low popularity, at a time when the chancellor is trying to claim a win from his government’s agreement on new measures meant to boost the flagging German economy.

“Spahn took liberties for himself he was willing to deny others,” said Cathryn Clüver Ashbrook, a German-American political analyst in Berlin. “That hypocrisy was simply too raw.”

In a resignation letter, Mr. Spahn expressed a degree of surprise at the controversy.

“In recent days, I have become aware that my personal happiness of starting a family and becoming a father together with my husband is not compatible with my political office,” he wrote.

He added that the tension between his private surrogacy decision and the expectations of him in his public role had become “greater than I expected.”