When he was a university student he was a pioneer activist in student's movements. After obtaining degree in 1994, he gave leadership to an active people movement called the "Janatha Mithuro" (The Friends of People) to defeat the then UNP government. He represented many advisory committees. In the 2015 general election, Rathana Thera was a national list nominee of the
United People’s Freedom Alliance. He was appointed to the parliament after
United National Party won the election. On 19 March 2019, he started a hunger strike in front of the Temple of the Tooth. It was initiated for being asked to step down the posts of the Minister
Rishad Bathiudeen, Governor of the Western Province
Azath Salley and Governor of the Eastern Province
M. L. A. M. Hizbullah. Then on 31 June 2019, Forty monks, including Rathana Thera, began a deadly hunger strike at the Temple of the Tooth for the same course. In the fourth day of fast he became hungry, and he ended his hunger strike after officially announcing the resignation of Azath Salley and M. L. A. M. Hizbullah from their posts. He was rushed to hospital and treated at the Surgical Intensive Care Unit of the Kandy General Hospital. On 19 June 2019, Rathana Thera lodged a written complaint with Acting IGP C.D. Wickremaratne against the Criminal Investigations Department where he has charged that the CID has failed to carry out a proper investigation into the allegations leveled against Dr. Shafi Shihabdeen from Kurunegala. On 18 December 2020, Rathana Thera was announced as the National List seat representative won by Our People's Party at the
2020 Sri Lankan parliamentary election. At the election, OPP polled 67,758 votes as a percentage of 0.58% and won one seat. On 5 January 2021, he sworn as the National List Member of Parliament and has decided to take a seat in the opposition party. ==Humanitarian efforts==