MOSTYN, Sir Roger, 5th Bt. (1734-96), of Mostyn, Flints. and Gloddaeth, Caern.

Published in The History of Parliament: the House of Commons 1790-1820, ed. R. Thorne, 1986
Available from Boydell and Brewer



26 Apr. 1758 - 26 July 1796

Family and Education

b. 13 Nov. 1734, 1st s. of Sir Thomas Mostyn, 4th Bt., by Sarah, da. and coh. of Robert Western of London. educ. Westminster 1745-51; Christ Church, Oxf. 1751. m. 19 May 1766, Margaret, da. and h. of Rev. Hugh Wynn, DD, preb. of Salisbury, h. of her uncles Robert Wynne of Bodysgallen, Caern., and Evan Lloyd Vaughan*, 1s. 6da. suc. fa. as 5th Bt. 24 Mar. 1758.

Offices Held

Ld. lt. Flints. 1761-d., custos rot. 1772-d.

Lt.-col. Flints. militia.


Mostyn retained the county seat unchallenged until his death. He continued to support the Whigs, appearing in the minority lists on Grey’s Oczakov motion, 12 Apr. 1791, and Whitbread’s motion against the Russian armament, 1 Mar. 1792; but was listed hostile to the repeal of the Test Act with regard to Scotland in April 1791. He did not succeed in an application to government in 1792 for the clerkship of the peace in Flintshire.1 In December 1792 he became a member of the Loyal Flintshire Association promoted by his brother-in-law Thomas Pennant of Downing.2 He was not listed a Portland Whig at that time, but he did not join Windham’s ‘third party’ either, though on Windham’s provisional list. No further minority vote is known until 30 Dec. 1794. The Duke of Portland must have thought he could influence Mostyn, who on 26 Nov. 1794 wrote to thank him for the news of the prorogation, which prevented Mostyn from keeping an appointment with the duke. With reference to this, Mostyn added that he should be sorry to differ from the duke but that unless an important issue came on in Parliament on 30 Dec., he felt no urge to be there.3 He came up and voted for Wilberforce’s amendment calling for peace. He again voted with opposition on the same question on 26 Jan. and 27 May 1795, but no other minority vote of his is known and he is not known to have spoken in debate. In the Treasury forecasts before the election of 1796, Mostyn was regarded as ‘pro’-government with hopes of future support. He died 26 July 1796, ‘much regretted and esteemed for his many public and private virtues’, having just been elected for the ninth time.4

Ref Volumes: 1790-1820

Author: R. G. Thorne


  • 1. PRO 30/8/161, f. 202.
  • 2. T. Pennant, Literary Life, 139; NLW mss 2586, Mostyn to Pennant, 14 Dec. 1792.
  • 3. Portland mss PwF6979.
  • 4. Gent. Mag. (1796), ii. 704.