On the death of his elder brother in 1801 Pierrepont succeeded to his seat unopposed, though there were some complaints about the honour becoming hereditary in the family.
Viscount Newark, as he was henceforward styled, supported the Portland ministry, moving the address, 26 June 1807. In August Canning thought of him as a potential under-secretary to him at the Foreign Office, but doubted if he would accept it.
Newark’s succession to the earldom in 1816 ended his family’s 38-year lien on a county seat for Nottinghamshire. He died 27 Oct. 1860.
