The emergency meeting of the Zanu-PF party is also removing first lady Grace Mugabe as head of the women’s league.
Senior figures in Zimbabwe’s ruling party stood and cheered as an official chairing the emergency meeting announced plans to remove Mugabe.
Obert Mpofu said Zanu-PF’s Central Committee members were meeting with “a heavy heart” because Mugabe had served the country and contributed to “many memorable achievements”.
But Mr Mpofu said in his opening remarks that Mugabe’s wife “and close associates have taken advantage of his frail condition” to loot national resources.
The 93-year-old Mugabe is meeting on Sunday with the army commander who put him under house arrest days ago in a second round of talks on his departure after nearly four decades in power.
Impeaching the president is another step when Parliament resumes on Tuesday, and lawmakers will “definitely” put the process in motion, the main opposition’s parliamentary chief whip said.
Innocent Gonese, of the MDC-T party, said they had been in discussions with the ruling Zanu-PF party to act jointly.
“If Mugabe is not gone by Tuesday, then as sure as the sun rises from the east, impeachment process will kick in,” Mr Gonese said.
Mugabe’s talks with army commander Constantino Chiwenga are the second round of negotiations on an exit as the military tries to avoid accusations of a coup.
Zimbabwean officials have not revealed details of the talks, but the military appears to favour a voluntary resignation by Mugabe to maintain a veneer of legality in the political transition.
Mugabe, in turn, could be using whatever leverage he has left to try to preserve his legacy as one of Africa’s liberation leaders or even protect himself and his family from possible prosecution.
Chris Mutsvangwa, head of the country’s liberation war veterans, said he was concerned that the military could end up opening fire to protect Mugabe from protesters. He vowed to “bring back the crowd” if the president did not step aside.
“We would expect that Mugabe would not have the prospect of the military shooting at people, trying to defend him,” Mr Mutsvangwa said. “The choice is his.”
The negotiations come ahead of a key ruling party congress next month, as well as scheduled elections next year.
Sunday’s talks do not appear to include the South African government delegation that took part in the first round. South Africa’s president on Saturday said talks are in “early days”.
The southern African regional bloc will hold a four-country summit in Angola on Tuesday to discuss the Zimbabwe situation.
Mugabe finds himself increasingly isolated under house arrest in his lavish Blue Roof mansion, deserted by most of his allies, with others arrested.
On Saturday, most of Harare’s population of 1.6 million poured into the streets in an anti-Mugabe demonstration that just days ago would have brought a police crackdown.
They clambered on to tanks moving slowly through the crowds, took selfies with soldiers and surged in the thousands toward the State House building where Mugabe held official functions, a symbol of the rule of the man who took power after independence from white minority rule in 1980.
The euphoria came after years of watching the once-prosperous African nation fall into decay, with a collapsing economy, repression of free speech, disputed elections and international sanctions.