[1] Upon the outbreak of the English Civil War Seymour joined the Royalist army, serving under his kinsman William, Marquess of Hertford.
[4] He accompanied Charles to Scotland in 1650, was voted away from the king's person by the Scottish committee, and left at Aberdeen after the defeat at Dunbar.
[7] In January 1654 he collected £1,920 for Charles in England, and received a pass on his return to France from the Lord Protector Oliver Cromwell.
He retired to Langley and died on 9 March 1686 aged 74, leaving his estate to his son Sir Henry Seymour.
His first marriage was to Elizabeth (died 1671), daughter of Sir Join Killigrew, and widow of William Basset, they had no children.