Ranawaka was active in politics while in university in the late 1980s as a member of the pro-JVP student union having spend over eight years as an undergrad in the university engaged in politics. He was arrested as part of the crackdown student activists during the JVP Insurrection in 1988 and again in 1991. He formed the Non-political organization called, 'Janatha Mithuro' with some of his colleagues like Ven.Athuraliye Rathana Thero, Nishantha Warnasinghe and Malinda Seneviratne. 'Janatha Mithuro' was criticized for its right-wing anti-Tamil ideology and actions. In the 1993 presidential elections they backed the People's Alliance headed by Chandrika Kumaratunga. He thereafter joined the Sihala Urumaya a Sinhala nationalist party. In 1998 he took part in forming the National Movement Against Terrorism. Sihala Urumaya evolved into the Jathika Hela Urumaya fielding Buddhist priests for the 2004 parliamentary elections and supporting Mahinda Rajapaksa in the 2005 presidential poll. In the 2015 presidential poll he supported Maithripala Sirisena and later join the United National Party led alliance.
Member of Parliament
Thereafter it becomes a partner in the Rajapaksa government in 2007. With it one of its Buddhist priest MP, Rev.Dr. Omalpe Thero resigned and his place was taken by Ranawaka as a national list MP who was thereafter appointed Cabinet Minister of Environment and Natural Resources by Rajapaksa. Ranawaka contested the 2010 General Election under the UPFA from Colombo District and was placed third place by obtaining 120,333 votes securing membership in the Sri Lanka Parliament and appointed to Minister of Power and Energy. In 2015 General Election Ranawaka contested under UNP from Colombo District. He was appointed the Minister of Megapolis and Western Development. He resigned on 18 November 2019.
Allegations of racism
In 2008 Ranawaka called the Muslim community in Sri Lanka 'outsiders' sparking widespread protests.
Criticism of international interventions
Ranawaka has also been critical of international intervention in Sri Lanka stating that anyone who takes action against Sri Lanka will be supporting terrorism. In April 2011 Ranawaka called the United Nation's report on alleged war crimes in Sri Lanka 'diplomatic terrorism'. Ranwaka has also opposed airstrikes against Libya.
Arrest
On 18 December 2019, he was arrested regarding his alleged involvement in a hit and run case which happened in 2016. He summoned in the Magistrate court the same day he was arrested and was initially remanded until 19 December 2019. He was further ordered by the court to be remanded until 24 December 2019.
Books
1991– End of Modern Development Paradigm limit to growth elaboration in sustainable development.