United Democratic Movement deputy leader and MP Roelf Meyer has quit 21 years of active politics, but says he will remain a member of the party.
Meyer said on Wednesday his decision was not easy and that he had agonised for some time before making up his mind.
"But the truth is the UDM is bigger than any one person. The party is well established with strong grass-roots support and a growing membership. It is in safe hands under the leadership of Bantu Holomisa."
Meyer insisted he was not defecting from the UDM.
"I am defecting from politics to do another job. This was a personal decision, not a political one."
Meyer declined to elaborate on his personal plans, but pledged that in his future work "I shall continue to hold sacred the principle that everything I do must be for the betterment of South Africa and its people".
"I shall devote, to the very best of my abilities, my services to the development of civil society in South Africa."
Meyer will quit parliament at the end of the month.
UDM leader General Bantu Holomisa paid tribute to Meyer, calling him a distinguished son of South Africa who had made an enormous contibution to its political life.
Meyer's departure would come as a surprise to many, but he had reached a watershed in his life.
The UDM owed a great deal to Meyer, Holomisa said.
It would take some time to find a new deputy, but the process was already under way. - Sapa