Prof Gillespie has published 16 books. The latest works have been Waste Policy: International Regulation, Comparative and Contextual Perspectives. (Edward Elgar, London, 2015); International Environmental Law, Policy and Ethics. (OUP, Second edition, 2015); and the Causes of War: Volume II (1000-1400) and Volume III (1400-1650), both published by Bloomsbury, NYC, 2017. The Long Road to Sustainability, published by Oxford University Press, Oxford, late 2017, is his most recent work. He has also written over forty academic articles.

Prof Gillespie has been awarded a Rotary International Scholarship, a Fulbright Fellowship, a residency at the Rockerfeller Bellagio Centre in Italy, and the New Zealand Law Foundation International Research Fellowship. His most recent award was from the Franqcui Foundation in Belgium, with which he held a professorship at Ghent University for six months during 2018/2019. He has also been the lawyer/expert on a number of international delegations and advised the New Zealand government on multiple matters of international concern. Professor Gillespie was the first New Zealander to be named Rapporteur for the World Heritage Convention, involving international environmental diplomacy under the auspice of UNESCO. Alexander has also been engaged in policy formation for the United Nations, the Commonwealth Secretariat, and governmental, commercial and non-governmental organisations in New Zealand, Australia, United States, United Kingdom, Ireland and Switzerland. He has also made a number of appearances before the Waitangi Tribunal and Select Committees of the New Zealand Parliament.