Thanks to the Irish Rebellion of 1641, Trevor's father was imprisoned in Narrowater Castle, where he remained until 1642 and died soon after being released.
[2] Following the outbreak of the First English Civil War, late in 1643, Trevor was part of a Royalist force which sailed to England, probably a division sent by the Marquess of Ormonde under Colonel Robert Byron, who garrisoned Chester.
[3] Trevor was soon given command of a regiment of horse, and in July fought at the Battle of Marston Moor, at which he was later claimed to have wounded Oliver Cromwell himself.
In October 1647 he was in Louth[5] but in June 1649 he deserted, following Monck's treaty with Owen Roe O'Neill, and rejoined the Royalists under Ormonde.
[2] In 1658 Trevor was trying to persuade others to support the future King Charles II, and before the Restoration, he was again firmly in the royalist camp.
On 27 March 1686, two of his sons matriculated at Christ Church, Oxford, and on 31 December 1687 John, the elder, was accidentally shot by his younger brother, Marcus Trevor.