Returned in 1751 for Whitchurch on the Selwyn interest, in 1754 Bertie was returned unopposed on the Ancaster interest at Boston, and was classed ‘for’ by Dupplin.
He served at Gibraltar in 1756, and at Byng’s trial testified in his favour. On 28 Apr. 1757 he made his only recorded speech in the House, declaring that the ten ships under Byng were not fully manned or provided with the necessary stores, and ‘insisting there was not a fire ship, tender, or hospital ship with the fleet’.
Bertie seems to have been uncertain about his position at Boston, and on 21 July 1760 pressed Newcastle for an office for one of his constituents because ‘the contest that I have at Boston makes it very essential to my interest to oblige this gentleman in this particular affair’.
In December 1762 he was counted by Fox among those favourable to the peace preliminaries, and in the autumn of 1763 was classed as ‘pro’ by Jenkinson. But in a list of Members drawn up 15 Feb. 1764 by Augustus Hervey is the remark: ‘is a doubt if he stayed it out’.
When in 1780 he had to stand a contest at Boston, he topped the poll. But again he was absent from all, even the most critical, divisions. On 28 May 1781 George Selwyn wrote to Lord Carlisle: ‘Lord Robert Bertie is again relapsed as I hear, and if so will probably last but a very little time.’
He died 10 Mar. 1782.
