Samaranayake was the Chairman of the Information and Communication Technology Agency of Sri Lanka from 2004.
He was also the Emeritus Professor of Computer Science of the University of Colombo and founder Director, University of Colombo School of Computing (UCSC) of the University of Colombo.
He served the University of Colombo for a continuous period of 43 years since his first appointment in 1961 immediately following his graduation from the same University.
Samaranayake had founded the Department of Statistics and Computer Science (DSCS) and of the Institute of Computer Technology (ICT) of the University of Colombo which were then merged as the UCSC in 2002.
A Fellow of the Harvard Information Infrastructure Project and the National Centre for Digital Government of the Kennedy School of Government, Harvard University, he was a Vis