 During the Wars of the Roses in his youth he was a Lancastrian supporter and took part in the conspiracy against King Richard III organised by the Duke of Buckingham.On the accession of King Henry VII (1485–1509) and at the end of the wars, Grenville was appointed one of the Esquires of the Body to King Henry VII.On the marriage of Prince Arthur to Katherine of Aragon on 14 November 1501 he was appointed K.B..