[2] Vane contested County Durham as a Whig on his family's interest at the 1722 British general election, but was unsuccessful.

At the 1727 British general election he planned to stand for county Durham, but stood down to avoid splitting the Whig vote, and the ministry found him another seat at St Mawes where he was returned as MP unopposed.

He became a follower of his kinsman, the Duke of Newcastle, cultivating him so assiduously that in 1749 he was appointed a Lord of the Treasury which he retained to 1755.

On 27 April 1753 he succeeded to the peerage as 3rd Baron Barnard on the death of his father and became Lord Lieutenant of Durham from 1753 to 1758.

He was rewarded by Newcastle with an earldom, as 1st Earl of Darlington and 1st Viscount Barnard on 3 April 1754 and held the post of Joint Paymaster of the Forces between 1755 and 1756.