He graduated from Southampton University in 1989 with a first class degree in English and Philosophy. In the early 1990s, he began publishing reviews, literary essays and articles in British newspapers and magazines before, in 1996, becoming a staff writer on The Times, during which period he was a judge of the Booker Prize for fiction. In the summer of 1998, he became literary editor of the New Statesman, later he was a contributing editor of the magazine. Meanwhile he continued to publish widely on an unusual range and combination of subjects, including literature, sport and politics.

In 2003, he became editor of The Observer Sport Monthly, which is acclaimed for the quality of its writing and photography. Under his editorship the magazine won numerous awards.

His novel, Unknown Pleasures, was published by Faber&Faber in 2000 and a second book, a work of narrative non-fiction called The Last Game: Love, Death and Football at the End of the Eighties, was published by Simon & Schuster in spring 2009.

His appointment as the New Statesman's editor was announced on 16 May 2008. and he returned in September 2008. Cowley's philosophy for the New Statesman was to explore ideas across the political spectrum, saying "I want to use the pages of the magazine to explore political ideas on both left and right." On 10 November 2009, he won the British Society of Magazine Editors’ Editor of the Year award in the Special Interest and Current Affairs Magazines category. The judges said that Cowley had transformed the New Statesman and "created issues of the magazine that were the envy of the industry".

In April 2010, Jason Cowley was shortlisted for the most coveted awards in the magazine industry, as Editor of the Year (consumer magazines) in the PPA Awards.