Lownie founded his eponymous literary agency in 1988. It specialises in non-fiction, representing some 200 authors, and is reported to have "regularly been the top selling agent in the world."[7] He founded, and is President of, The Biographers' Club,[8] a group "committed to supporting, promoting and connecting biographers at all levels."[9]
In 2021, Lownie published The Traitor King, a biography, based on fresh sources, of the Duke of Windsor. The former Edward VIII is alleged by Lownie to have been a Nazi sympathiser who gave aid and comfort to his country’s enemies before and during the Second World War.[17]
Lownie also wrote a literary guide to Edinburgh,[18] and has edited several volumes of John Buchan's works.