不久以後,托利黨內有關解放天主教的紛爭冷卻下來,卡蘇里於是在1802年重返政府,出任管理委員會主席(President of the Board of Control)一職。在1804年,經過他的大力遊說,小皮特得以重任英國首相,而卡蘇里則出掌陸軍及殖民地大臣一職。但小皮特不久卻在1806年因故逝世,卡蘇里於是隨「賢能內閣」的成立而辭職。然而,「賢能內閣」僅存活了一年多,便在紛亂之中垮台,到1807年,新任首相波特蘭公爵重新任用卡蘇里為陸軍及殖民地大臣。可是,卡蘇里其後卻與時任外相喬治·坎寧在瓦爾赫倫長征(Walcheren Expedition)大敗一事上出現紛爭,兩人事後更在1809年展開決鬥,結果兩人都被迫辭去政府職務。
^Macquarie, Lachlan. Thursday 6th. Decr.. Journal of a Tour of Governor Macquarie's first Inspection of the Interior of the Colony Commencing on Tuesday the 6th. Novr. 1810. [2020-02-10]. (原始内容存档于2009-10-20) –通过Macquarie University.
^Castlereagh River. Geographical Names Register (GNR) of NSW. Geographical Names Board of New South Wales. [18 January 2013].
伸延閱讀
Harold Nicolson, 'The Congress of Vienna' 1946
H. Montgomery Hyde, 'The Strange Death of Lord Castlereagh'
John Derry, 'Castlereagh' London 1976
Wendy Hinde, 'Castlereagh' London 1981
Henry Kissinger, 'A World Restored: Metternich, Castlereagh and the Problems of Peace, 1812-22'
Charles Webster
Robert Stewart, 'The Lightning Rod for Lord Liverpool's Government: Lord Castlereagh and HIs Critics, 1812 to 1822' Unpublished M.A. Thesis, The University of Western Ontario, London, Ontario 1993