Gruffydd was the son of Gwilym ap Rhys and Catrin verch Elidir. The date and place of his birth have not been found.
His wife was Dyddgu verch Thomas. They were married, but the date and place have not been found. Their two known children were Ieuan ap Gruffudd (?-?) and Efa verch Gruffudd Goch (?-?).