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

Published in The History of Parliament: the House of Commons 1754-1790, ed. L. Namier, J. Brooke., 1964
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.  educ. Westminster 1745-51; Ch. Ch. Oxf. 1751.  m. 19 May 1766, Margaret, da. and h. of Rev. Hugh Wynne, preb. of Salisbury cathedral, and h. to Robert Wynne and Evan Lloyd Vaughan, 1s. 6da.  suc. fa. 24 Mar. 1758.

Offices Held

Ld. lt. Flints. June 1761- d.; custos. rot. 1772- d.


Mostyn succeeded his father in the representation of Flintshire, and held the seat without opposition for the rest of his life. On his entry into the House he joined the court Whigs, with whom his uncle, General John Mostyn, was connected, and in 1761 Newcastle sent him his parliamentary whip. It is uncertain how he voted over the peace preliminaries: his name appears in a list of the minority among the Bute mss, but not in the printed lists. He voted against general warrants, 18 Feb. 1764, and was on the whole averse to the Grenville Administration. He supported the Rockinghams, and adhered to them in opposition.

Mostyn retained an independent attitude, however. On 3 Feb. 1769 he voted for Wilkes’s expulsion, but on 15 Apr. and 8 May against seating Luttrell. He voted against the Spanish convention, 13 Feb. 1771, but for the next seven years or so seems to have inclined towards Administration. In February 1779, on the contractors bill, he was marked as a Government supporter, but from then onwards went into systematic opposition, and before the general election was considered by Robinson as an opponent. In the new Parliament he acted with the Rockinghams on most questions, yet he voted for the peace preliminaries, 18 Feb. 1783. After that he supported the Coalition, both in office and in opposition. Thomas Pennant, his brother-in-law, criticized him for his attitude, complaining that he had broken his promise made in 1780 to ‘enlist under no party, follow no set of men’:1

Your saying that the present majority is not anti-monarchical is saying nothing, for if you deprive the King of the power of choosing his own servants ... you make him merely nominal. There is not a wish to change our representative, provided he acts consonant to our principles; but none of us ought to give up principle for affection ... The great majority of your constituents are firm friends to the legal prerogative. They will re-elect you; yet how they must blush at their inconsistency if you take an adverse part.

After 1784 he continued to support Fox and voted with the Opposition on the Regency bill.

He died 26 July 1796.

Ref Volumes: 1754-1790

Author: Peter D.G. Thomas


  • 1. T. Pennant, Literary Life, 95.