The ruling, which was handed down on Thursday will affect all Xitsonga marriages concluded after May 30, and will not affect those concluded before that date.
According to experts called in to give evidence before the court, in the Xitsonga tradition it is customary to get the consent of the first wife – or at the very least to inform her – when the husband decides to marry another woman.
But, citing the constitutional principles of human dignity and equality, the court ruled that going forward, the first wife in a Xitsonga marriage must consent to having an additional wife in the marriage, in order for a subsequent marriage to be valid.
"Are the first wife's rights to equality and human dignity compatible with allowing her husband to marry another woman without her consent? We think not," said the court.
It said "any notion of the first wife's equality with her husband would be completely undermined if he were able to introduce a new marriage partner to their domestic life without her consent".
The court was ruling on a matter concerning the rights of two women – Modjadji Mayelani and Mphephu Ngwenyama – the first and second wives of Hlengani Moyana, who died in 2009.
After his death, both women tried to have their marriages legally recognised by the department of home affairs. Ngwenyama, the first wife, also sought to have the second marriage declared void as her husband had not informed her of it or sought her consent, as is customary.
A Supreme Court ruling last year found both marriages to be valid, even though they had not been registered in accordance with the Recognition of Customary Marriages Act.
But the ruling handed down by the Constitutional Court on Thursday overturns that finding.
"The customary marriage between Hlengani Dyson Moyana and the first respondent, Mphephu Maria Ngwenyama, is declared null and void," the court found.
This, it said, was because the second marriage was not concluded in accordance with Xitsonga customary laws — the first wife was never informed of the second marriage, much less given her consent.
Difference of opinion
While the judges of the Constitutional Court were unanimous in agreeing that the second marriage in this particular case was invalid in terms of Xitsonga law, they were split on the question of whether the court should have taken steps to develop the customary law to require that the first wife give consent for the second marriage.
A minority judgement written by Judge Chris Jafta, with Judges Mogoeng Mogoeng and Bess Nkabinde concurring, said: "Undisputed facts show that Xitsonga customary law followed by the relevant community already requires consent of the first wife. This alone renders the development of the rule unnecessary."
Judge Raymond Zondo held a similar view.
The court recognised that one potential problem with the ruling, which is effective from June, is that members of the public may not be aware of its effects on the way Xitsonga marriages must be concluded.
It ordered that a copy of the judgement and a summary of its contents be made available to the House of Traditional Leaders and to the minister of home affairs for further distribution. How quickly the information will be disseminated in Xitsonga communities remains to be seen.
Jennifer Williams, director of the Women's Legal Centre, which entered the matter as a friend of the court, said she was pleased that the court had developed the customary law based on equality and dignity.
"The only concern I have is this [ruling] has to be published and distributed. If it invalidates marriages where there is no consent, we have to look at what protections can be put in place to protect women," she said
"Women may not know the man is already married and women don't always have the power to bargain around these things."
Williams said it she was also pleased that the court had reaffirmed that failure to register a customary marriage does not invalidate that marriage. This was the starting point for the centre's involvement in the case.
"Our concern has always been that women shouldn't be prejudiced or lose out on property rights because the validity of their marriage is questioned," said Williams.
The judgement could provide clarity for women who may agree to being in polygynous Xitsonga marriages going forward, but for Ngwenyama it is a fruitless end to a long struggle for recognition.
Achmed Mayet, a Legal Aid lawyer acting for Ngwenyama said the ruling came as a shock.
"I still have to communicate this to the client. It will be a shock for her as well," he said.
"The estate will now be wound up and she and her children will get nothing because they are saying her marriage is invalid."
Mayet said he believed the judgement would cause untold hardship for those married both before and after it was handed down.
"Who is to say that in all the marriages concluded prior to 30 May 2013, the first wife was informed and by whom?" he asked.
For marriages yet to be concluded, Mayet questioned whether a court would in fact be able to establish whether a first wife had given consent for additional marriages.