[2] Horner was a prefect and served on numerous committees including the yearbook, debating, cadets, and student christian movement.
[6] Horner has a Diploma of Military Studies from Duntroon, a Master of Arts (Honours) from the University of New South Wales, and graduated with a Doctor of Philosophy from the ANU in 1980.
Horner authored or co-authored the second and third volumes: Australia and the 'New World Order' (2011) and, with John Connor, The Good International Citizen (2014).
A team led by Horner also won a tender to write the official history of the Australian Security Intelligence Organisation (ASIO).
[5] In 2009, he was appointed a Member of the Order of Australia for his "service to higher education in the area of Australian military history and heritage as a researcher, author and academic.