Tangwystl was the daughter of Gruffudd ap Ednyfed and Angharad verch Dafydd. The date and place of her birth have not been found.
Her husband was Iorwerth ap Gruffydd. They were married, but the date and place have not been found. Their three known children were Gwladys verch Iowerth (?-?), Efa verch Iorwerth (?-?) and Gwen verch Iorwerth (?-?).