The deputy president of the Patriotic Alliance, Kenny Kunene, will be a Johannesburg councillor under the leadership of the new mayor, Thapelo Amad.
It is not yet clear which of the eight party councillors the 52-year-old will replace.
This was confirmed by Amad ahead of the announcement of his executive, which is set to take place on Thursday or Friday.
Amad was elected as mayor after a vote of no confidence in Mpho Phalatse.
He was put up for election after a decision in November that a minority party member should become the leader of the then opposition coalition.
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Up until Thursday, the opposition parties were split regarding the leadership decision, with Amad, of Al Jama-ah, and Margaret Arnolds, of the African Independent Congress, as the candidates. The parties have three and two seats respectively.
Gauteng Premier Panyaza Lesufi said the decision came after lively arguments at caucus breaks during the council sitting.
Despite being sworn in on Monday, Amad is yet to announce his executive.
Now that Kunene is set to be a councillor, he can be elected to the mayoral committee.