The Protector summoned him in 1657 to his House of Lords, but he was imprisoned in 1659 on suspicion of a share in Booth's insurrection and, after the Restoration, was created, in 1661, earl of Carlisle, Viscount Morpeth and Lord Dacre of Gilsland, titles which are still held by his descendants.
There is evidence that he "was settled in Morpeth as a Presbyterian minister as early as 1709."
At Morpeth Horsley opened a private school.
He gave lectures on mechanics and hydrostatics in Morpeth, Alnwick and Newcastle, and was elected F.R.S.
In the following year he entered parliament as member for Morpeth, but for a considerable period he took scarcely any part in the debates.