Prof. Prematilleke held many important positions in professional bodies during his lifetime. These enabled him to make numerous lasting contributions to archaeology and related fields.
- Sectional Secretary and Pro-tem President, 20th Anniversary of the International Council of Museums (ICOM) / Second International Campaign of Museums 1968
- Member, Committee on the Development of Archaeological Education at the Universities, National Council of Higher Education, 1970
- Member, Panel of Experts on Buddhist Art – Ceylon National Committee for UNESCO, Ministry of Education 1970
- University of Peradeniya
- Chairman – University Arts Council, 1971-82
- Chairman – Sub-committee on Film and Drama, 1974-75
- Representative, Committee on sculpture and Painting, 1975-76
- Member – Library Committee of The Faculty of Arts – 1977.
- Acting Head – Department of Languages and Cultural studies – June to December 1977
- Convenor, Sub-committee on Course in South Asian Studies, Faculty of Arts
- Member, Evaluation Committee, Faculty of Arts
- Member, Curriculum Committee, Faculty of Arts
- Chairman – University Arts Council, 1971-82
- Archaeological Survey of Sri Lanka
- Member, Advisory Committee on Protected Monuments (1970-79)
- Director, Conservation of the Nalanda Gedige (1979-85)
- Member, Advisory Board on Archaeology, 1970-75 (in charge of restorations of Gadaladeniya and Mirisavatiya) and 1990 onwards
- Vice-President, Archaeological Society of Sri Lanka, 1976-79, and subsequent Committee Member Archaeological Soceity of Sri Lanka (archaeology.org.lk)
- Member, Committee on Conservation and Development of Historic Sites and Monuments under the Accelerated Mahaveli Development Scheme, 1978.
- Member, Board on the Cultural Triangle of Sri Lanka November (appointed in 1979)
- Member of the sub committee on ‘Dutugemunu’s Ashes’ – MInistry of Cultural Affairs, 1979
- Member, Advisory Board on National Museums, Department of National Museums 1968-71 and 2007-10
- Member, Advisory Committee – National Museum Kandy (1979 – 81)
- Co-Director, Research Project on the Vatadage in Polonnaruwa, with Professor Takeshi Nakagawa, Waseda University, Tokyo, 1983-1985
- Member, Committee to make Kandy a World Heritage site – approved by UNESCO in 1988
- UNESCO – Sri Lanka Cultural Triangle programme: Archaeological Director, Polonnaruva (1980-99) and Kandy (1981- 99) projects
- Scientific Leader(3rd Leg) – UNESCO Spice Route of the Silk Road of the Sea (Colombo to Madras, Phuket, Malacca, Surabhaya and Bangkok) 1990
- Director, Excavation of Skeletal Remains in Fua Mulak, Maldives, sponsored by the Republic of Maldives, 1986.
- Director of project for preparation of an Inventory of Places of Religious and Cultural Significance and Areas of Scenic and Recreational Value, Coast Conservation Department, Sri Lanka, 1986.
- Postgraduate Institute of Archaeology (PGIAR, University of Kelaniya)
- Senior Co-Coordinator (with Prof.Senake Bandaranayake) at its inception (then Postgraduate Centre of Archaeological Studies) 1986
- Member – Board of Governors until 1987
- Chairman – Research and Publications unit until 1987
- Member – Board of Studies from 1990
Speaking at the PGIAR Archaeometallurgy conference organized with Peradeniya in 1987
- Sri Lanka Council of Archaeologists
- Founder President (1989-90)
- Committee member (2000-01)
- Chairman of academic board
- Member of disciplinary committee
- International Council on Monuments & Sites (ICOMOS)
- Co-Chairperson, Publications Committee, ICOMOS Sri Lanka 1993
- Organized first ICOMOS International (Asian) conference in Sri Lanka, 1993
- President – ICOMOS National Committee, Sri Lanka 1997 – 2000
- Honorary Member – ICOMOS (International) since 2018 (the first Sri Lankan to receive it)
- Member of the Organizing Committee (and editor of catalogue) for the exhibition titled “The Heritage of Sri Lankan Bronze Sculpture”, held at the National Museum, Colombo 1995
- Member – Academy of Sri Lankan Culture (1996)
- Chairman – National Committee for the Exhibition of Sri Lankan Artefacts in Tokyo, 2008
- Member, Advisory Board on Archaeology, Department of Archaeology, Ministry of Cultural Affairs, Sri Lanka 2002-15
- Chairperson, Committee for the Maritime History and Archaeology Museum, Galle Fort, 2007
- Co-chairperson of the subcommittee on Museums, Museology and Culture-in-development, Asia-Pacific Institute of Museology and Culture-in-development (UNESCO) 2003.
- Member – Committee to review the work of Department of Archaeology, October 2013
- Central Cultural Fund
- Editorial Board member for the CCF bulletin and Research Coordinator (1989)
- Coordinating Director and later Consultant, Publications unit – 1993 to 2005
- Chairman, Evaluation Committee on Publications.
- Editorial Consultant for all publications of CCF
- Chairman, Editorial Board, History and Archaeology Series.
- Advisor, CCF Printing Press
- Wrote proposal for establishment of a Research Centre at the CCF in 2002, and subsequently served as a Senior Member of its Steering Committee
- Supervision of the CCF library
- Chairperson, Translations Committee of the Classical Sinhala Text Translation series (link to publications)
- Life Member of the Royal Asiatic Society of Sri Lanka
With staff of the CCF publications unit