He is also the chairman of the Sri Lanka Tourism Promotion Bureau (SLTPB).
The Tourism Development Authority is a policy making and infrastructure development agency.
SLTDA said in a statement that Gunarathna is director general of the Development Forum Office of Sri Lanka's economic development ministry, which is in charge of tourism.
He was the former director of the National Zoological Gardens.
Nalaka Godahewa who was recently appointed chairman of Sri Lanka's Securities and Exchange Commission resigned as chairman of the tourism authority last week.
Questions have been raised about conflicts of interest over Godahewa's connections to a firm which was planning to build a hotel.