Jacob Zuma, the polygamous president of South Africa, is to gain his third first lady in a traditional Zulu wedding on Monday.

Zuma, 67, will marry Tobeka Madiba in a private family ceremony at his homestead in rural KwaZulu-Natal province, the president's office confirmed. Madiba, 36, will be Zuma's third current wife and his fifth marriage overall. He is also reported to be engaged to another woman.

The Zulu tribe, the biggest ethnic group in South Africa, practises polygamy by tradition. Zuma once told an interviewer: "There are plenty of politicians who have mistresses and children that they hide so as to pretend they're monogamous. I prefer to be open. I love my wives and I'm proud of my children."

The wedding is scheduled for 6am local time and goats and sheep have been slaughtered for the feast, South Africa's Sunday Times newspaper reported. Zuma is expected to vow to love and protect Madiba, with whom he has three children, in a Zulu ceremony known as udwendwe. She will become South Africa's third first lady, joining Sizakele Khumalo-Zuma, whom Zuma has known for 50 years and married in 1973, and Nompumelelo Ntuli-Zuma, whom he married two years ago.

There were two further wives who are no longer with him. He divorced Nkosazana Dlamini-Zuma, now home affairs minister, in 1998. Kate Mantsho Zuma killed herself in 2000, after describing her marriage to him as "24 years of hell". Zuma is said to have more than 10 children, and possibly as many as 19. Zuma has paid lobolo to the family of Madiba, described as a socialite from Durban, as custom demands. She has attended official events with the president but it appears the wedding has been postponed until now because of Zuma's work commitments. He was elected president in April.

No known date has been set for what could be Zuma's sixth wedding. Gloria Bongi Ngema is understood to have presented umbondo (gifts) to the Zuma family last week, customarily a precursor to marriage. Originally from Durban, Ngema works for IBM in Johannesburg and has a son with Zuma named Sinqumo.

South African law recognises multiple marriages, although fewer young South Africans are entering into them because they are seen as expensive and old-fashioned. The cultural practices of Zulus and other groups are protected by the constitution. Zuma played up his Zulu heritage during the election campaign and spent Christmas at his homestead in Nkandla, in KwaZulu-Natal. He relaxed by shooting birds with a slingshot, drinking umqombothi (traditional beer) and taking part in a chess tournament. It emerged this month that a reported R65m (£5.3m) expansion of the Nkandla residence is under way with new houses being built to accommodate Zuma's three wives. Jeremy Gordin, Zuma's biographer, said he was surprised how little attention Zuma's latest wedding had received. "I find it interesting that there were all kinds of people making belligerent comments on his polygamy, but that died down after the election."