In the 1970s he wrote regularly for the New Statesman on fiction and for The Times and Plays and Players on theatre, and he has published since in many newspapers and magazines including The New Yorker and Granta.
Franco's Crypt: Spanish Culture and Memory since 1936 (2013), published in Spanish by Ariel in 2015, was described by Antonio Muñoz Molina as "A book that must be read, in Spain and abroad, by anyone who wants to understand the country" and by Stanley Payne in The Wall Street Journal as "the best, and most objective, brief introduction to Spain's memory wars to be found in any language."
His most recent book is Mr Straight Arrow: the Career of John Hersey, author of 'Hiroshima' (New York: Farrar, Straus & Giroux, 2019).
The American Scholar said of it, "This admirable book about an admirable man… belongs to that elegant, reticent, wholly non-sleazy, and sadly disappearing genre known as literary biography, and for anyone interested in how a writer’s life is really lived as opposed to its incidental moments of glamour, Jeremy Treglown’s account of Hersey’s career—its constraints and opportunities, the worries and satisfactions, and the nature of the actual work—is deeply satisfying."
Treglown also wrote the first full biography of Roald Dahl, and initiated and, with Deborah McVea, co-edited the online index of previously anonymous contributors to the TLS.