Tahir, 31, was picked by the Proteas to play against England in January last year but was later withdrawn from the squad because he had not fulfilled residency requirements in his new home.
"Imran has made South Africa his home and has been married for some time to a South African. He has been a leading wicket taker in the top South African domestic competitions for the past few seasons and is highly respected by both his colleagues and his opponents," CSA chief executive Gerald Majola said in a statement.
"He certainly becomes a contender for selection to the Proteas squad now that he has met all the government, International Cricket Council and CSA regulations regarding his new nationality."
The well-travelled Tahir, who has taken 535 first class wickets at an average of 25.09, plays for the South African franchise KwaZulu-Natal Dolphins and has represented Middlesex, Yorkshire and Hampshire in English county cricket.
