South Africa's parliament will vote by secret ballot on a motion of no confidence on President Jacob Zuma, the legislative body's speaker announced.
The surprise announcement on the vote, which could end Mr Zuma's presidency, was made by National Assembly Speaker Baleka Mbete at a news conference in Cape Town.
She said her decision shows that parliament is responsive to the public.
"The people of South Africa look to parliament to give direction in challenging times. The people of South Africa also look to parliament for signals of hope," said Ms Mbete, a long-time Zuma ally.
Mosiuoa Lekota, leader of the opposition Congress of the People, described the secret ballot as "ground-breaking".
"It places the responsibility of the motion of no confidence squarely on the shoulders of the men and women who sit in the National Assembly," Mr Lekota told reporters.
Scores of anti-Zuma protesters marched through Cape Town to the parliament building on Monday.
Larger demonstrations, both for and against Zuma, are planned for Tuesday at the parliament building before the vote.
Opposition parties have lobbied for months for an anonymous no-confidence vote to provide cover to disgruntled members of Mr Zuma's African National Congress who may fear coming out against their leader in an open ballot.
The motion, which was introduced by the opposition Democratic Alliance, needs 201 out of 400 votes to succeed.
The ANC holds 246 parliamentary seats, but several members have already indicated publicly that they will vote against President Zuma.
In June, the nation's highest court said it was up to the speaker of parliament to decide whether the vote could be done by secret ballot.
President Zuma, dogged by corruption scandals and waning popularity, has faced public calls for his resignation by leading members of his own party, the African National Congress.
The ANC has told its politicians to vote against the motion, intending to use its parliamentary majority to back Mr Zuma, as it has in earlier attempts to oust him.
"Voting in favour of this motion will be tantamount to throwing a nuclear bomb at our country," an August 4 statement from the office of ANC Chief Whip Jackson Mthembu said.
In recent weeks, two ANC politicians who publicly said they intended to vote against President Zuma were quickly censured by the party.
Mr Zuma has survived six earlier no-confidence votes since becoming president in 2009.