He played a significant part in events during and after the English Civil War in South Wales, siding first with King Charles, then with the Parliamentarians, before rejoining the Royalists in 1648.
Trevor Williams was a descendant of a marriage in 1300 between Howel Gam ap David of Penrhos Castle and Joyce, a daughter of the Herefordshire based Scudamore family.
Sir Charles, Trevor's father, was a noted Puritan who presented a fine Jacobean pulpit with the text "Woe Be to Me if I Preach not the Gospel" to Caerwent church in 1632.
At the outbreak of what was to become the First English Civil War, this gave him responsibilities for raising an army within Monmouthshire for the King, and holding the county against opposition.
After his release, he set about fortifying the ruined medieval Tregrug Castle at Llangibby, beside the Caerleon to Usk road, and garrisoned it with 60 men.
[1][3] As a tenant of the Earl of Pembroke, as were his family before him, he naturally took up the shared feud with the successive holders of the title Duke of Somerset.
As a result, in 1648 he helped Sir Nicholas Kemeys, 1st Baronet and Custos Rotulorum of Monmouthshire, to seize and hold Chepstow for the King.
[4] By 1683 he was accused of fomenting trouble among the youth of Monmouthshire, and in 1684 Beaufort successfully sued him and his ally John Arnold for scandalum magnatum, libel against a peer.