The Ghanaian midfielder, who spent last season on loan at Mpumalanga Black Aces from SuperSport United, has long been sought after by the Buccaneers.
Reports suggest he joined Pirates in camp ahead of the Carling Black Label Cup, having only recently returned from his homeland.
Gyimah becomes Bucs’ seventh off-season signing after Gift Motupa (Baroka FC), Felipe Ovono (Deportivo Mongomo, Equatorial Guinea), Tendai Ndoro (Mpumalanga Black Aces), Luvuyo Memela (Cape Town All Stars), Thembinkosi Lorch (Maluti FET College) and Roger Majafa (Polokwane City).
Get the latest Pirates news sent to your phone. SMSs cost R1.50.