Chief Justice Mogoeng Mogoeng, however, stopped short of ordering a secret ballot, saying it would be a violation of the separation of powers between the Constitutional Court and parliament.
Speaker Baleka Mbete, a top ANC official, had said parliamentary rules did not allow for a secret ballot but Chief Justice Mogoeng Mogoeng disagreed, saying she had "the necessary latitude".
President Zuma has survived four no-confidence votes during his eight years in power
South Africa's top court ruled on Thursday that the Speaker of Parliament can order a secret ballot for no-confidence motions, an outcome the opposition hopes would embolden ANC MPs to rebel and depose scandal-plagued President Jacob Zuma.
However, Chief Justice Mogoeng Mogoeng stopped short of ordering a secret ballot, saying it would be a violation of the separation of powers between the Constitutional Court and parliament.
Zuma, who will be in parliament later on Thursday, has survived four no-confidence votes during his eight years in power thanks to loyal voting by African National Congress (ANC) lawmakers, who form a strong parliamentary majority.
But opposition parties believe a recent cabinet reshuffle that led to the dismissal of respected finance minister Pravin Gordhan and a slew of credit rating downgrades may have angered ANC MPs sufficiently to desert Zuma.
Speaker Baleka Mbete, a top ANC official, had said parliamentary rules did not allow for a secret ballot but Chief Justice Mogoeng Mogoeng disagreed, saying she had "the necessary latitude".
Crass dishonesty
In a unanimous ruling by the full bench, he said a vote in parliament should not be "a fear or money-inspired sham", and urged the Speaker to consider the interests of the country, rather than party, when deciding the nature of the vote.
"Crass dishonesty in the form of bribe-taking or other illegitimate methods of gaining undeserved majorities must not be discounted from the Speaker's decision process," he said.
"When that happens in a motion of no-confidence, the outcome could betray the people's interests."
After the ruling, the rand pared its gains to 0.5 per cent against the dollar from 1 per cent earlier. The currency had firmed on hopes Mogoeng would order, rather than simply permit, a secret vote.
Stepping down
The president has recently faced unprecedented criticism from senior ANC figures, including Deputy President Cyril Ramaphosa.
Mr Zuma, who came to office in 2009, is due to step down as head of the ANC in December, and as national president ahead of the 2019 General Election.
He is seen as favouring his ex-wife, former African Union chief Nkosazana Dlamini-Zuma, to succeed him — rather than Ramaphosa.
The case was brought by the United Democratic Movement (UDM), the Economic Freedom Fighters (EFF) and the Congress of the People (COPE) last month, asking the court to give parliament the go-ahead to vote in secret against the president.
The debate around the fifth motion of no-confidence was scheduled for April following President Zuma’s controversial Cabinet reshuffle, but it was postponed by the Speaker on the request of opposition parties to wait on the outcome of the court’s decision.
Justice Mogoeng ordered that both President Zuma and Ms Mbete should cover the costs of the case brought by the UDM and other parties.
The ANC has said it will vote against the motion to remove the 75-year old leader. A successful vote of no-confidence would trigger the collapse of Zuma's government.
-Additional reporting by Peter Dube, Africa Review.
