McKellar actively facilitates physics research, policy development and international collaboration globally, especially in the Asia-Pacific Region. He served on the board of trustees of the sia Pacific Centre for Theoretical Physics and on the Council of the Association of Asia Pacific Physical Societies for many years. He chaired the Regional Committee for Asia and the Pacific of the International Council for Science (ICSU) (2009–2011), as well as the Australia and New Zealand Association for the Advancement of Science (ANZAAS) (1992–1998).