A Zanu-PF official said a motion to strip him of the presidency would be presented to parliament on Tuesday, and the process could take just two days.
The motion accuses the 93-year-old of charges including allowing his wife Grace to “usurp constitutional power”.
Military leaders, who last week intervened, said he will meet his exiled former vice-president soon.
Emmerson Mnangagwa fled Zimbabwe after Mr Mugabe stripped him of his position, seen by many as a way clearing the way for his wife to succeed him as leader.
The move riled top army officials, who stepped in and put Mr Mugabe under house arrest, though he nominally remains the president.
The military said they have planned a “roadmap” with Mr Mugabe for the future.
On Sunday, despite intense pressure Mr Mugabe surprised many by refusing to resign, instead in a TV speech vowing to preside over next month’s Zanu-PF party congress.
Impeachment proceedings are set to go ahead after a deadline set by the party for Mr Mugabe to stand down came and went.
Speaking outside a party meeting on Monday, member of parliament Paul Mangwana said of the president: “He is a stubborn man, he can hear the voices of the people, but is refusing to listen.”
Impeachment in Zimbabwe can only occur in specific scenarios, on grounds of “serious misconduct”, “violation” of the constitution or “failure to obey, uphold or defend” it, or “incapacity”.
“The main charge is that he has allowed his wife to usurp constitutional power when she has no right to run government. But she is insulting civil servants, the vice president, at public rallies. They are denigrating the army – those are the charges,” Mr Mangwana said.
“He has refused to implement the constitution of Zimbabwe – particularly we had elections for the provincial councils, but up to now they have not been put into office.
He added that the process – which some experts had thought would be lengthy – could be fast-tracked and completed by Wednesday, “because the charges are so clear”. (Courtesy BBC)