Fitzroy, a pro-Catholic Whig, had represented Thetford on the interest of his half-brother the 4th duke of Grafton in the 1812 Parliament, making way there in 1818 for his nephew Lord Charles Fitzroy*.
Lord John was foreman of the special jury that declared the 3rd earl of Portsmouth insane (since 1809), 28 Feb. 1823. The law commissioners had rejected his plea for exemption from serving on account of the ‘great inconvenience which might result to him in the discharge of his public duties and as a Member’.
