HARARE, Zimbabwe — It was the resignation speech that did not happen.

Robert Mugabe, 93, who ruled Zimbabwe with an iron grip until the military took over and placed him under house arrest, stunned the nation on Sunday night with a nearly 20-minute address in which he refused to say whether he would resign.

Many political observers and fellow Zimbabweans had been waiting for Mr. Mugabe to step down as president after nearly 40 years in power. But sitting at a table while flanked by members of the military and other officials — including a priest — the embattled president said he would preside over the party congress, scheduled to take place in a few weeks.

“I will preside over its processes, which must not be prepossessed by any acts calculated to undermine it or to compromise the outcomes in the eyes of the public,” he said.

But observers questioned how he could oversee the conference if he was no longer leader of the party.

Many Western news outlets had alerted the world to a pending resignation, citing confidential sources. But it was not to be — at least in the speech on Sunday night.

Mr. Mugabe made the rambling, halting televised address to the southern African nation about 9 p.m. local time after intense negotiations at the State House with the country’s Army generals about the conditions of his what was expected to be his departure.

Among the men sitting off to the side was the very army commander, Constantino Chiwenga, who had placed him under arrest. Mr. Mugabe spoke for a little more than 18 minutes, sometimes repeating phrases and appearing to lose his place among the pages before him.

The address came hours after he was expelled as leader of his own governing party, ZANU-PF, which gave him until noon Monday to resign or face impeachment by Parliament.

The day before, thousands of Zimbabweans had taken to the streets to celebrate Mr. Mugabe’s seeming fall from power after the military seized control but was careful not to call it a coup.

Party officials earlier on Sunday removed his wife, Grace Mugabe, widely viewed as his likely successor, as head of the ZANU-PF Women’s League and barred her from the party for life.

It also appointed Emmerson Mnangagwa, the vice president previously fired by the president, as Mr. Mugabe’s successor to lead the party.

The stunning rebuke by the central committee of Mr. Mugabe’s party, ZANU-PF, came after emergency

Under the Constitution, Mr. Mugabe remains president after the party’s decision on Sunday. But leaders had threatened that if he did not resign by noon Monday, he would face impeachment by Parliament.

Cheers and dancing broke out in the building after the decision to expel the party leader who had ruled Zimbabwe for 37 years.

“There is a case at the end!” a group of youths chanted after storming an open space outside the ZANU-PF headquarters. They sang a phrase that loosely translated to “We lead on while they bark.”

Announcing the expulsion of Mr. Mugabe, Patrick Chinamasa, the party’s secretary for legal affairs, said: Mr. Mugabe “hereby is recalled as first secretary and president of the ZANU-PF party. He is therefore asked to resign forthwith.

“In the event that the resignation would not have been tendered by midday 20th of November, 2017, the ZANU-PF chief whip was ordered to issue proceedings for the removal of the president in terms of Section 97 of the Constitution of Zimbabwe Amendment Number 20.”

Before the committee’s decision, Chris Mutsvangwa, a war veteran who has led the campaign to oust Mr. Mugabe as party leader, said as he went into the meeting, “We are going all the way,” according to Reuters.

He said that Mr. Mugabe should just resign and leave the country: “He’s trying to bargain for a dignified exit but he should just smell the coffee.”

The central committee also expelled the president’s wife, Grace Mugabe, as head of the ZANU-PF Women’s League. Mrs. Mugabe, widely viewed as his likely successor, has not been seen in public since Wednesday.

Mrs. Mugabe, a former typist who had amassed wealth and power in the governing party, was barred for life from the party. So were Jonathan Moyo, Zimbabwe’s minister of higher and tertiary education; and Saviour Kasukuwere, the minister of local government, along with several others.

The downfall of the autocratic ruler began with a military takeover on Wednesday. Once respected as a liberation icon who went into exile after fighting colonial rule, Mr. Mugabe became isolated from fellow party officials. Zimbabwe’s only leader since the country gained independence from Britain in 1980, he previously had faced little opposition from the party rank and file.

But the military placed him under house arrest, saying it wanted to target the criminals around Mr. Mugabe who had pillaged the country’s economy. And veterans of the fight for independence from white-minority rule joined the march on Saturday as Zimbabweans poured into the streets and danced, sang and shouted with joy at the prospect of Mr. Mugabe’s rule ending.

Mr. Mugabe met on Sunday for a second round of talks with the military. The president, who has resisted stepping down, sought to negotiate a dignified departure, the Zimbabwe state-run broadcaster said.

mediated. Others on the negotiating team included the deputy director-general for the Central Intelligence Organization, Aaron Nhepera, and the Mugabe spokesman George Charamba.

A majority of the party’s leaders had recommended expelling Mr. Mugabe — a slap at the man who had controlled the organization with an iron grip.

In a resolution, party leaders said Mr. Mugabe should be removed for taking the advice of “counterrevolutionaries and agents of neo-imperialism”; for mistreating his vice president, Mr. Mnangagwa; and for encouraging “factionalism.”

It urged the “immediate and unconditional reinstatement” of Mr. Mnangagwa, at least until the national elections scheduled for next year.

On Sunday, the leaders put force behind their recommendations. ZANU-PF’s central committee did not spare Mr. Mugabe’s second deputy president, Phelekezela Mphoko, who was also fired after serving as a vice president for three years.

The committee also elevated Mr. Mnangagwa to fill the vacancy left after the dismissal of Mr. Mugabe as party leader. Mr. Mnangagwa was nominated as the party’s sole presidential candidate for the 2018 elections, a position the committee said would be confirmed by the party’s congress in December.

Mr. Mugabe had fired Mr. Mnangagwa in a move that positioned Mr. Mugabe’s wife to succeed him as president. But the firing may have been an overreach by the Mugabes, as it singled out an erstwhile ally with liberation-war credentials and strong support from the military.