In 1450 on his marriage to his first wife, Elizabeth Cobham (died 1453), he gained the seat of Myddle Castle, Shropshire, as a dowry.
He fought in the Battle of Blore Heath on 23 September 1459, killing the Lancastrian commander Lord Audley.
In 1484, he was appointed for life as Escheator and High Sheriff of Merionethshire and made Constable of Harlech Castle.
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".
His Coat of Arms was: Quarterly of six: Roger gave his name to the estate of Plas Kynaston, lands which he also owned in Cefn Mawr, North Wales.