Nagle served as a soldier in Vietnam 1966-1968. He has worked as a screenwriter in the film industry, including in the USA and Great Britain, since 1979, and has received a number of awards. His only novel, The Odd Angry Shot, was made into a feature film in 1979, with a screenplay adaptation by Tom Jeffrey. His other film credits include the screenplay for Death of a Soldier (1985), co-authorship (with Tony Johnston) of the screenplay for The Siege of Firebase Gloria (1988) and on-screen presenter of 'The Van Beelen Case' (1987), an episode of the series of crime investigation documentaries Beyond Reasonable Doubt.