In 1755 Peachey was returned for Seaford on the Treasury interest, at the recommendation of Lord Lincoln, Newcastle’s nephew and heir.
He was not a candidate at the general election of 1768. Immediately after Newcastle’s death Lord Pelham asked him as an old friend of Newcastle to stand at Seaford with Government support. ‘Although’, he wrote on 20 Nov. 1768, ‘there might have been some little difference in politics, you had a mutual regard and esteem for each other.’ Peachey replied the next day: ‘It is not less pleasing to me to find that he had retained some favourable opinion of me, however the confusion of past times might have misrepresented my regard to his person. I therefore ... gladly accept your obliging offer, and hope your nomination of me will meet with a general approbation at Seaford, for I must own to you that I am not yet restored to that robust state of health which can enable me to undertake a contest.’
He died 1 Feb. 1808.
