32-year-old De Villiers was appointed in January following Hashim Amla's resignation as skipper.
De Villiers, 32, was appointed in January following Hashim Amla's resignation, and led the team in two Test matches against England before injury forced him to miss the series against New Zealand and Australia.
South Africa lost one Test and won one under De Villiers. In his absence Faf du Plessis impressed with his leadership as stand-in skipper during back-to-back Test wins over Australia.
"The interests of the team must always outweigh the interests of any individual, including me," said De Villiers, who backed Du Plessis.
"It was a fantastic honour for me to be asked to captain the Test side but I have missed two series and I am still in doubt for the upcoming series against Sri Lanka.
"Following the squad's outstanding performances in Australia, it is clearly in the greater interests of the team that Faf du Plessis should be confirmed as the permanent Test captain.
"I have known Faf for almost 20 years, ever since we played in the same school side at Afrikaans Hoer Seunskool, and he will have my unequivocal support if he is asked to continue leading this exciting Proteas Test team."
De Villiers has been ruled out of the three-match Test series against Sri Lanka after failing to recover sufficiently from his elbow injury.
Meanwhile, Du Plessis' appeal against a ball-tampering sanction will be heard before the International Cricket Council (ICC) on December 19.
An ICC panel found Du Plessis guilty after footage emerged from the second Test in Hobart that showed him applying saliva to the ball with a mint in his mouth.