Lord Robert Montagu was brought in as a Whig for the county by his brother, the Duke of Manchester, in 1734, though Sarah, Duchess of Marlborough, refused her support because ‘I know what your Grace has been obliged to vote and likewise what my Lord Robert Montagu must vote for the same reason’.1HMC 8th Rep. pt. 2 (1881), p. 110. His only recorded vote was in favour of the Administration on the Spanish convention in 1739. At the time of his marriage Lord Hervey, his ‘brother vice-chamberlain’, wrote to Henry Fox:
What will Miss Harriet make Ld. Robert besides a husband, a father and a penitent? There are few improvements his head will allow of; but I dare say she knows his wants as well as her own so well that all the improvement in her power will be amply bestowed.2Lord Ilchester, Lord Hervey and his Friends, 225.
He succeeded to the dukedom in October 1739, but lost his family’s electoral pre-eminence in the county to his kinsman, the 4th Earl of Sandwich, and was unable to nominate candidates for the 1747 and 1754 Parliaments.3See HUNTINGDONSHIRE. He died 10 May 1762.