Pietersen will be available for five games for the Durban-based Dolphins from the start of November, returning to the team he left as a youngster to pursue a career in England.
"It's wonderful. All my buddies are there, my best mates are there ... It's going to be fun," the England batsman said of his return to his hometown team.
Pietersen, now 35 and apparently discarded by England for good despite being its record run-scorer, was born in Pietermaritzburg, near Durban.
He said he will return late next month ahead of the Ram Slam competition. He will be available for the Dolphins for around two weeks, he said.
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"It's a great comeback, but its work," Pietersen said, adding he would "try to leave emotion out of it."
The move was announced a day after England director of cricket Andrew Strauss said the Ashes-winning team had "moved on" from Pietersen, seemingly closing the door on any return.
"I would love to play cricket for England again but for the moment that's a no-go," Pietersen said in South Africa.
"My mind is nowhere near that tour. In all honesty, I couldn't give you an answer," he said.
Pietersen spent part of his holiday with former South African test players Graeme Smith, Jacques Kallis, and Mark Boucher, and Smith's role as the Ram Slam's tournament director helped pave the way for Pietersen's move.