Mugabe had faced growing pressure to resign since last week, when the military took over state institutions and the ruling ZANU-PF party called on him to step aside.
Zimbabwe's president Robert Mugabe has resigned, the parliament speaker has said.
Following the army's intervention last week in response to Mugabe's sacking of vice president Mnangagwa, it has become clear that Mugabe's 37-year tenure as the Zimbabwean president will shortly come to an end amid widespread demands for his resignation.
"Given the events that followed my dismissal I can not trust my life in President Mugabe's hands".
Zimbabwean president Robert Mugabe has resigned. Denis Balibouse Reuters
Emmerson Mnangagwa (75), the vice president whom Mr Mugabe sacked earlier this month for showing "traits of disloyalty", is expected to be installed as Zimbabwe's new leader within 48 hours.
Mugabe's announcement was an acknowledgment of the inevitable.
But Mugabe refused to resign, prompting the impeachment procedure which would have been the only legal was to force him out.
It had been feared that Mugabe's 52-year-old wife Grace would succeed her husband as leader, but it now appears as though it is only a matter of time before Mr Mnangagwa takes over as president. The plot posited an interim unity government with worldwide blessing to allow for Zimbabwe's re-engagement with the world after decades of isolation from global lenders and donors.
Mnangagwa was initially believed to be in South Africa.
But many say he has damaged Zimbabwe's economy, democracy and judiciary by staying in power for too long and has used violence to crush perceived political opponents.