He was invested as a knight of Order of the Garter in 1633.
He married Mary Villiers, daughter of George Villiers, 1st Duke of Buckingham on 3 August 1637.
A third cousin of Charles I of England, Stewart was a Privy Councillor and key member of Royalist party in the English Civil War.
In 1641β42, he served as Lord Warden of the Cinque Ports.
He spent five months in exile in 1643, returning to England to defend the city of Oxford for the king.
He died on 30 March 1655 at age 42 and was buried in Westminster Abbey.