The 35-year-old midfielder joined the Clever Boys as a free agent on Wednesday after parting ways with English side Sunderland AFC last week.
Pienaar, who is a childhood Pirates fan, held informal talks with the club last year before he joined Sunderland prior to the 2016/17 season.
The Johannesburg-born player recently disclosed that he would be open to signing for the Soweto giants.
However, the Clever Boys have since signed Pienaar, who spent 16 years in Europe playing in Holland, Germany and England.
Pienaar and football fans took to Twitter after Wits announced the news:
I'm officially a Clever Boy — Steven Pienaar (@therealstevenpi) July 5, 2017
Pienaar is the 'biggest name' signing in the PSL after Bennie signed with Pirates but I use biggest name signing loosely here. — Philasande Sixaba (@psixaba) July 5, 2017
When someone says Thamsanqa (sp) Sangweni is better than Steven Pienaar.
Meaning Pirates got a better player than Bidvest Wits. — Charlie Cesc Makgoba (@CWharlie4) July 5, 2017