He was elected as a Member of Parliament for Cambridge University while still under age in 1774 and remained in that constituency until he moved to the House of Lords when he succeeded his grandfather.
He married on 26 December 1775 at St George's, Hanover Square, London, Lady Mary Isabella Somerset, fifth and youngest daughter of Charles Noel Somerset, 4th Duke of Beaufort, and his wife, Elizabeth Berkeley. She was born 1 August 1756.
They had the following children, (with perhaps a daughter, who died young);
Lady Elizabeth Isabella Manners, born 28 September 1776, died 05 October 1853, married 21 August 1798, Richard Norman, Esq, of Leatherhead, Surrey.
John Henry Manners, born 04 January 1778, succeeded his father as 5th Duke of Rutland
Lady Katherine Mary Manners, born 22 April 1779, died 10 March or 01 May 1829, married 17 June 1800, Cecil Weld Forester, 1st Baron Forester;
Major General Lord Charles Henry Somerset Manners, born 24 October 1780, died unmarried 25 May 1855;
Major General Lord Robert William Manners, born 14 December 1781, Lieutenant-Colonel 3rd Dragoons, died unmarried 15 November 1835;
Lord William Robert Albanac Manners, born 01 May 1783, died just before his tenth birthday, on 22 April 1793.
↑ Cokayne, has 21 February, Brydges, p. 489; Namier; Lodge, p. 347 have 15 March.
↑ She is not mentioned by Barker, and Brydge, who list all the other children, or Lodge, but Namier states had 4 sons & 3 daughters
↑ names and dates from Barker; Lodge, p. 347; Brydges, p. 489
Barker, George Fisher Russell, 'Manners, Charles, fourth Duke of Rutland (1754-1787)' in Dictionary of National Biography, 1885-1900, vol 36. Digitised by Wikisource (http://en.wikisource.org/ : viewed 05 April 2014).
Brydges, Sir Egerton (ed?), (1812), Collins's Peerage of England; Genealogical, biographical and historical, vol. 1 (of 9); London : PC & J Rivington. Digitised by Google Books (http://books.google.com), from The Library of the University of California; downloaded 27 May 2009.
Cokayne, G.E., (1895) Complete Peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, extant, extinct or dormant, vol 6, London : George Bell & Sons.
Lodge, Edmund, (1859), The Peerage and Baronetage of the British Empire, as at Present Existing, 28th ed. revised and enlarged, London: Hurst and Blackett. Digitised by Google Books (http://books.google.com).
Namier, Sir Lewis, (1964), 'Manners, Charles, Mq of Granby (1754-87)', in The History of Parliament: the House of Commons 1754-1790, ed. L. Namier, J, Brooke; digitised The History of Parliament: British political, social & local history (http://www.historyofparliamentonline.org/ : viewed 05 April 2014)