Tharanga comes in as a replacement to Kumar Sangakkara, who will not be available for selection for the final Test match.
Minister of Tourism and Sports Navin Dissanayake ratified the decision of the selectors.
Sri Lanka defied the weather gods and a strong Pakistan bowling line up to clinch a commanding 7 wicket win over the visitors and level the 3 match series to 1-1 at the P Sara Oval grounds yesterday.
The Lankans after a moral shattering tour opener loss will head to Pallekelle on Friday to clinch the series win.