In 1454 Kynaston was the Constable of Denbigh Castle and High Sheriff of Shropshire in both 1461 and 1470.
Guto'r Glyn, the Bard of Valle Crucis Abbey (1445-1475) wrote a "cywydd" in Kynaston's honour entitled "Syr Rosier Cinast o'r Cnewin".