After a career in the Commons which included opposition to George Villiers†, duke of Buckingham, and support for Thomas Wentworth†, earl of Strafford, Seymour was elevated to the peerage in February 1641. A royalist during the civil wars, he was a substantial landowner, with his income being assessed at £3,000 in November 1645 and £5,000 in August 1646.
At the Restoration Seymour sought to re-establish his political interest in Wiltshire and at Westminster. He was reinstated as a privy councillor and as chancellor of the duchy of Lancaster and set about recovering crown property, writing on 21 Sept. to Walter Aston, 2nd Baron Aston of Forfar [S], about embezzlement at Tutbury Castle.
On the eve of the Convention, Philip Wharton, 4th Baron Wharton, listed Seymour as one of the ‘Lords with the king’. Seymour took his seat on 22 May 1660, being named to a committee charged with formulating a reply to the Commons on the issue of the Lords’ right to vote on the question of legal proceedings against the regicides. Two days later he was appointed to draw up a letter of congratulation upon the king’s safe landing in England. On 31 July 1660 he was absent from a call of the House, even though the Journal records his presence. On 21 Aug. he was one of three peers added to the committee which had managed the conference with the Commons on the bill of indemnity, in order to prepare heads for a further conference.
Seymour was known to be strongly in favour of punishing all the regicides, but on 25 Aug. he was named to a small select committee to consider the Commons request for a proviso to the indemnity bill saving some of them.
Seymour was present when the Convention resumed on 6 Nov. 1660, but attended only until the end of the month, 16 days in all, around 36 per cent of the total. He was named to a further three committees. It was probably at this point that he registered a proxy in favour of Robartes, a peer with whom he shared many committee appointments. Seymour re-established his political interest in Wiltshire when his son, Charles Seymour, later 2nd Baron Seymour of Trowbridge, was returned for the county seat in 1661 in partnership with Henry Hyde, later 2nd earl of Clarendon.
Seymour was present at the opening of the Cavalier Parliament on 8 May 1661. He was listed as absent from a call of the House on 20 May, despite his attendance being recorded in the Journal. On 11 July he was thought to be an opponent of the case of Aubrey de Vere, 20th earl of Oxford, to be lord great chamberlain. He attended on 55 days of the session before its adjournment at the end of July 1661, nearly 86 per cent of the total, and was named to nine committees.
Seymour was present when the session resumed on 20 Nov. 1661. He attended regularly until the Christmas adjournment on 20 Dec. but then did not reappear in the House until 7 Mar. 1662. There was a further gap in his attendance between 20 Mar. and 11 Apr. 1662. He attended on the last day of the session, 19 May, having been present on 47 days of that part of the session, nearly 36 per cent of the total.
Seymour first sat on the second day of the 1663 session, 19 February. On 23 Feb. he was absent from a call of the House, and although he attended on the 25th he was then absent until 9 April. He was reckoned by Wharton on 13 July to be a likely opponent of the attempt by George Digby, 2nd earl of Bristol, to impeach the lord chancellor, Edward Hyde, earl of Clarendon.
Seymour attended on the second day of the 1664 session, 21 March. He was present on 12 days of the session (just over 32 per cent of the total), being named only to the committees for privileges and petitions. He last sat in the Lords on 14 May, shortly before the session’s adjournment. He died on 12 July 1664, ‘resigning himself up very quietly’,
