He was initially left out because of a foot injury but proved his fitness on the England Lions tour of the United Arab Emirates, playing in two Twenty20s against Pakistan A last weekend.
“I've been really pleased with the way things have gone with the Lions,” Finn said in a news release on Monday.
“I've bowled my overs and my foot has come through fine. I'm excited by the prospect of linking up with the team out in South Africa.”
Finn, 26, played the last of his 26 Tests against Australia at the Oval in August.
The second Test against South Africa will be played in Cape Town from January 2, with further matches in Johannesburg (January 14-18) and Pretoria (Januar 22-26). – Reuters
Original source: Finn added to England squad