Milsington was returned as
Member of Parliament for
Wycombe on the Wharton interest at a by-election on 1 February 1726 but on account of the partiality of the returning officer, the election was declared void on 22 February. At the subsequent rerun of the by-election on 3 March he was again returned as MP through the partiality of the returning officer, but was unseated on petition on 17 March. At the
1727 British general election he was returned as MP
Andover in a contest. He voted with the Administration on the civil list arrears in 1729. On 2 January 1730 Milsington succeeded to the peerage on the death of his father and vacated his seat in the
House of Commons. In February 1732, he was sent as envoy to Don Carlos, when he took possession of Parma and Piacenza. He was made a knight of the
Order of the Thistle on 2 June 1732. From 1734 to 1737, he was a Scottish representative peer in the House of Lords.
Society Portmore was a leading racehorse owner and owned among others,
Crab and
Squirt. He became well known in high society for the splendour of his dress and equipages. He was a founding Governor of the
Foundling Hospital, a charity created in 1739, dedicated to the salvation of
abandoned children. ==Personal life==