At the end of the First English Civil War in 1646, he accompanied the future Charles II of England into exile and fought with him at the Battle of Worcester in 1651.
Honors awarded to Wentworth included being created a Knight of the Bath and appointment to the Privy Council of England (PC).
His daughter, Henrietta, succeeded to the barony upon her father's death; she would have an affair with James Scott, 1st Duke of Monmouth, but no children.
He saw action at Tipton Green, Cropredy Bridge, and possibly at Newbury, all in 1644; at Langport in 1645; and at Worcester, the final battle of the English Civil War in 1651.
After the fall of that garrison, he joined the King's Main Field Army, and as Lord Wentworth, raised a company of dragoons.
Consequently, Wentworth followed suit and on 5 February 1644, he succeeded Sir Thomas Byron as colonel of the Prince of Wales's Regiment of Horse.
After Goring's defeat at Langport and subsequent dismissal, Wentworth was appointed major-general of horse under the western army's new commander, Lord Hopton.
Charles was compelled to subscribe to the Solemn League and Covenant as a condition of being recognized as King, but many of his followers neglected to do so including Wentworth and his father.
Despite the defeat of the Scots army at Dunbar on 3 September 1650, both Wentworth and his father were, as non-subscribers, ordered out of the country on 17 October.
In 1656 in Bruges, he was responsible for organizing and commanding a regiment of foot guards that served as a bodyguard unit to the exiled king.