Research Fellow, California Institute of Technology, 1965.
Honorary Professor, University of Buckingham, UK.
Honorary Professor University of Ruhuna, Sri Lanka.
Visiting Professor, University of Peradeniya, Sri Lanka.
Honorary Professor, Sir John Kotelawala Defence University, Sri Lanka.
Adjunct Professor, National Institute of Fundamental Studies, Sri Lanka.
Editor in Chief, Journal of Astrobiology and Outreach.
Board Member, Institute for the Study of Panspermia and Astroeconomics.
Professor of Mathematics, Vidyodaya University of Ceylon, 1966.
Visiting Professor, Universities of Arizona and Maryland USA, 1966-1970.
Visiting Professor, Yukawa Institute, Kyoto University, Japan, 1969.
Tutor and Supervisor in Mathematics, Jesus College, Cambridge.
Member of the Graduate Staff, Institute of Theoretical Astronomy, University of Cambridge, 1966-1973.
Visiting Professor, University of Western Ontario, London, Ontario, Canada, 1974 and 1976.
Director, Institute of Fundamental Studies, Sri Lanka, 1982-1984.
UNDP Consultant/Advisor, President of Sri Lanka, 1982-1984.
Visiting Professor, Institute of Space and Astronautical Studies, Japan, 1993.
Visiting Professor, University of the West Indies, Mona, Kingston, 1994.
Professor and Head of the Dept.of Applied Maths and Astronomy, University College, Cardiff, 1973-1989
Professor of Applied Mathematics and Astronomy, Cardiff University, 1990-2006
Professor and Director, Cardiff Centre for Astrobiology 2006-2011
Visiting Fellow, Churchill College, Cambridge 2015-2016.
