‘Schillo’ has started training with the side, just as he was mulling a return to the Premier Soccer League with Orlando Pirates reportedly keen to bring him back to South Africa.
Pienaar was signed twice by Moyes at Everton and the Scot is a known admirer of the former Bafana Bafana skipper.
Moyes was appointed by The Black Cats last week and is looking to beef up the attacking play for the North East side.
Pienaar has had a tough 18 months with injuries but when he was given a chance at Everton last season looked to be back to something like his lively the best.
The 34-year-old was not offered a new contract though and is a free agent.
He has been the subject of some interest from Pirates and Mamelodi Sundowns, but both those could be frustrated by the new opportunity that has opened up for him in England.