In 1981 he wrote articles on the civil war in El Salvador, published in The Age, The Sydney Morning Herald and the (London) Observer.

In 1999, Kingsbury led the Australia East Timor International Volunteer Program monitoring mission to Timor-Leste's 'popular consultation' for independence.

The mediator of these peace talks, former Finnish President Martti Ahtisaari, was awarded a Nobel Peace Prize in October 2008, 'for his efforts on several continents and over more than three decades', including playing a prominent role in resolving many conflicts in Namibia; Aceh, Indonesia; Kosovo and Iraq, among other areas'.

In 2014 Kingsbury returned to El Salvador to research the publication Gold, Water and the Struggle for Basic Rights in El Salvador (Oxfam Australia, 14 September 2014) which contributed to the International Center for Settlement of Investment Disputes dismissing a claim by Pac Rim Cayman LLC against El Salvador in regard to its freedom to mine under the North America Free Trade Agreement (NAFTA), being the first time the NAFTA provisions had been defeated in court.

He was Vice-President/Deputy Chair of the Balibo House Trust until late 2024 [7] and formerly a Director on the Board of the East Timor Hearts Fund.