De Silva said SLT would continue roll out communications technology to benefit customers.
"I hope to build and add value to the good work that the former CEO of SLT started and I am cognizant of the extremely dynamic and experienced team SLT possesses," De Silva said in a statement.
"We will work together to consolidate the SLT Group’s premier position in Sri Lanka."
De Silva was chief executive of Mobitel from 2011 and had been advisor to chairman of SLT from 2002 to 2004.
The company said he had been at IBM in Sri Lanka and Australia and at Saudi Telecom and been a advisor to Sri Lanka. He is a graduate in electronic and telecommunications engineering and a Fellow member of the Institute of Management Consultants, UK.