Dunraven was back at Versailles for the signing of the Treaty of Versailles in 1919, which ended World War 1.
As an Irish peer he was a member of the House of Lords, where he sought to improve the rights of Irish tenant farmers and to resolve demands for Home Rule, hoping to keep Ireland in the United Kingdom.
Upon the foundation of the Irish Free State he became a member of the first Senate in December 1922 serving until his death in 1926.