The 35-year-old joined Bidvest Wits at the start of the 2017/18 season, but was released by the club in the January transfer window.
Pienaar confirmed his retirement on Sport At 10 on SABC on Wednesday evening.
The midfielder has represented the likes of Everton, Sunderland, Borussia Dortmund, Ajax Amsterdam and Tottenham Hotspur abroad, winning two Dutch Eredivisie titles.
Pienaar also made 61 appearances for the national side, where he represented the nation at two World Cups, the FIFA Confederations Cup and the Africa Cup of Nations.