Prior to this until March 2009 he was the Special Representative of the Secretary-General heading MINURSO Western Sahara.
Harston lectures all over the world to distinguished military and civilian audiences, and takes a leading role in War Games and Exercises for NATO, Pinnacle/Pyramid in Riga and for the UK, most recently Joint Venture 2018 in Cyprus, German, Serbian, Swedish, Canadian and Ugandan armed forces.
In January 2012 Harston delivered a Strategic Review for the UN Security Council on UNIFIL, the peacekeeping operation in Lebanon.
In August 2013 he was asked to make a presentation to the government committee reviewing Swiss Security Policy in Bern Switzerland.
His other interests include Early English Church music and a 1952 Series One Land Rover.