After the Acts of Union 1707, the position of Privy councillor was abolished, but he was returned as Member of Parliament for Aberdeenshire at the 1708 British general election.
As the eldest son of a peer, however, he was declared ineligible and was replaced by Sir Alexander Cumming, 1st Baronet a year later.
After the change of administration in 1710, he applied for a place and was granted an unpaid role as a Scottish Commissioner of chamberlainry and trade in 1711.
[1] In about 1716, Lord Haddo married, as his second wife, Lady Susan Murray, daughter of the 1st Duke of Atholl.
[1] In addition to his political career, Lord Haddo was instrumental in the architectural development of his estates, notably completing Haddo House, near Tarves in Aberdeenshire in 1732, which was designed by William Adam and remains a significant example of early 18th-century Scottish architecture.