Knightley's main professional interests were war reporting, propaganda, and espionage. In more than 30 years of writing about espionage, he met most of the spy chiefs of all the major intelligence services in the world, and interviewed numerous officers and agents from all sides during the Cold War and since.
For over three decades, Knightley dedicated his career to reporting on espionage, meeting with many of the world's top intelligence officials during the Cold War and afterward. He conducted interviews with a wide range of spies and intelligence officers from various countries.