Aslet was educated at Peterhouse, Cambridge, where he earned a degree in the history of architecture. After graduating, he joined Country Life magazine in 1977 as architectural writer, becoming architectural editor in 1984, deputy editor in 1989, and editor-in-chief in 1993. In 1997 he was named British Society of Magazine Editors' Editor of the Year. After 13 years as editor-in-chief, from 13 March 2006, Aslet left and took on a newly created role of editor-at-large, leading Country Life's important public relations activities and acting as an editorial consultant and writer for the magazine, as well as writing more books and doing freelance articles for newspapers such as the Daily Telegraph, the Daily Mail, and the Sunday Times, and broadcasts on radio and television current affairs programmes such as Newsnight.

Aslet lives in London and Ramsgate with his wife and three children.

Aslet is the author of:

• The Last Country Houses (Yale University Press, 1982) (ISBN 0300029047). Paperback edition 1985 (ISBN 0300034741)
• Quinlan Terry: The Revival of Architecture (Viking, 1986) (ISBN 0670808318)
• The National Trust book of the English house (with Alan Powers; Harmondsworth Penguin, 1986) (ISBN 0140065083)
• Deuce of an Uproar: William Eden Nesfield's Letters to the Rector of Radwinter in Essex (Friends of Radwinter Church, 1988) (ISBN 0951374605)
• Knight Frank & Rutley's Buying a Country House: A County Guide to Value (Country Life, 1989) (ISBN 1852770635)
• The American Country House (Yale University Press, 1990) (ISBN 0300047576). Paperback, 2005 (ISBN 0300105053)
• The American Houses of Robert A.M. Stern (with Robert A.M. Stern; Rizzoli International Publications, 1991) (ISBN 0847814335)
• Countryblast (with Michael Heath; John Murray, 1991) (ISBN 0719549450)
• Anyone for England? (Little, Brown; 1997) (ISBN 0316881724)
• Inside the House of Lords (with Derry Moore) (HarperCollins, 1998) (ISBN 0004140478)
• The Story of Greenwich (Fourth Estate, 1999) (ISBN 1857028252)
• A Horse in the Country: Diary of a Year in the Heart of England (Fourth Estate, 2001) (ISBN 1841153753). Paperback, 2002 (ISBN 1841153761)
• Landmarks of Britain: The Five Hundred Places That Made Our History (Hodder & Stoughton Ltd, 2006) (ISBN 0340735112)
• The English House (Bloomsbury Publishing, 2008) (ISBN 0747577978)