Then on Tuesday, members of ZANU-PF introduced a motion of impeachment, invoking a constitutional process that had never before been tested.
The party’s historical political rival, the Movement for Democratic Change, seconded the motion, a striking sign of the consensus in the political class that Mr. Mugabe must go — one that formed with astonishing speed after the military took Mr. Mugabe into custody last Wednesday, signaling an end to his 37-year rule.
Debate on the impeachment motion had begun when the speaker suddenly interrupted the proceedings to read what he said was a letter of resignation delivered by Mr. Mugabe’s representatives.
In Africa Unity Square, the capital’s main public area, scattered shouts were heard just a few minutes after the announcement by the speaker. Then, as word began spreading by mouth and by phone, the shouts, cries and honking of cars rose in a deafening crescendo. Hundreds of people ran to the square, hugging and jumping, as the crowd soon swelled into the thousands.
“I’m happy,” said Presca Nzendora, 32, a street vendor who was hugging a friend, jumping up and down. “Bob has resigned! We were starving because of him.”
Bryan Moyo, 30, who works in internet security, ran into the middle of the square in his dark suit and red tie. “Thirty-seven years is not a joke,” he said. “He’s the only president I’ve ever known. It’s indescribable. It’s been hell. I feel like we’ve been liberated a second time.”
Nicholas Nyamaka, a 65-year-old taxi driver, said, “I used to think it would never come. It’s a dream come true. So finally the suffering is over.”
For nearly four decades, Mr. Mugabe managed to stay at the helm by handing out the spoils of power to his allies — and by crushing dissent. He oversaw the massacre of thousands of civilians in the 1980s and outmaneuvered rivals in his party and in the opposition. Even in his 90s and weakened by age, he kept potential successors at bay.
But he pushed too hard by trying to position his wife, Grace Mugabe, 52, as his successor. She entered politics only two years ago, had no role in the nation’s liberation war and treated with open contempt politicians who had been waiting decades to succeed her husband.
The chain of events leading to Mr. Mugabe’s downfall started on Nov. 6, when he fired his vice president, Emmerson Mnangagwa, a close ally of the military, and then tried to arrest the nation’s top military commander a few days later.
Mr. Mugabe had finally come down against the military and its political allies in a long-running feud inside the governing party.