Cooke was born on 20 April 1945, second son of Dr Basil Cooke and Nancy Irene Cooke (née Neal). He was educated at the private Framlingham College, Suffolk. He went on to study at Peterhouse, Cambridge, from which he graduated Master of Arts (MA Cantab) in 1970. He was a lecturer and tutor in modern history at The Queen's University of Belfast from 1971 to 1977 and was awarded a PhD from that institution in 1979.^[4]

Cooke worked as a desk officer within the Conservative Research Department from 1977 to 1983. During this period he served as political adviser to Airey Neave, Shadow Secretary of State for Northern Ireland, 1977–79. He joined the Conservative Political Centre in 1983 as assistant director, becoming deputy director two years later and Director between 1988 and 1997.

He was appointed an Officer of the Order of the British Empire (OBE) in the 1988 New Year Honours.^[5] He was a founder, in 1997, and member since 2005 of the Conservative Party Archive Trust. He was Chairman of Trustees of the pressure group Friends of the Union between 1995 and 2003 and has been Senior Trustee of the T. E. Utley Memorial Fund since 2000.

Cooke was made a life peer as Baron Lexden, of Lexden in the County of Essex and of Strangford in the County of Down, on 23 December 2010^[6] on the recommendation of Prime Minister David Cameron. He sits in the House of Lords as a Conservative.

Lord Lexden's website highlights his work in the Lords, including speeches, videos, letters and articles for numerous publications, including ConservativeHome and The House magazine.^[7]

Lexden is a frequent contributor to many national newspapers, offering a historical context to modern political life.

With the Conservative return to opposition in 1997, Cooke worked as General Secretary of the Independent Schools Council from 1997 to 2004 and later became President of the Independent Schools Association.^[8] He has also been a Governor of The John Lyon School Harrow from 1999 to 2005 and Patron of the Northern Ireland Schools Debating Competition since 2001. He is a frequent contributor The Times Letters and Obituary pages.

Lexden is an occasional television guest presenter. In 2019, he presented a BBC TV programme called Prime Properties about former Prime Minister Stanley Baldwin^[9]

As a member and historian of London's Carlton Club, Lexden objected to the Club's hanging of a portrait of former Prime Minister Boris Johnson on the grounds that Johnson had "brought discredit on the highest political office". The painting was duly removed and rehung in the Club's "Cad's Corner".^[10]

• Lord Carlingford's Journal (1971) (joint editor)
• The Governing Passion; Cabinet Government and Party Politics in Britain 1885–86 (1974) (joint author)
• The Ashbourne Papers 1869–1913 (1974) (editor)
• The Conservative Party's Campaign Guides (7 vols, 1987–2005) (editor)
• The Conservative Party: Seven Historical Studies, (1997) (editor)
• The Conservative Research Department 1929–2004 (2004) (editor)
• The Carlton Club 1832–2007 (2007) (joint author)
• Tory Heroine: Dorothy Brant and the Rise of Conservative Women (2008)
• A Party of Change: a Brief History of the Conservatives (2008)
• Between the Thin Blue Lines (2008)(contributor)
• Tory Policy-Making: the Conservative Research Department 1929–2009 (2009) (joint author)
• A Gift from the Churchills: The Primrose League 1883–2004 (2010)

As well as pamphlets on Northern Ireland and constitutional issues and articles in historical journals and educational publications.

• Who's Who 2011

• Alistair Lexden's official website