Entering politics in 1983 as a Member of Parliament from Maharagama and later Colombo, his first role in government was as Minister of Transport under Ratnasiri Wickremanayake.

In 2022, Gunawardena was appointed the Prime Minister after former President Gotabaya Rajapaksa resigned amidst the ongoing economic crisis and Ranil Wickremesinghe was elected as his successor.

from the University of Oregon, and whilst in the United States, became involved in student activism, taking part in anti-Vietnam War protests.

[10] After graduation from the University of Oregon, Gunawardena worked in New York City, but returned to Sri Lanka in 1972 after his father's death.

[12][13] During the 1989 parliamentary election, Gunawardena successfully ran as one of the MEP's candidates in the multi-member Colombo Electoral District.

[33] On 22 July 2022, Gunawardena was appointed Prime Minister after former President Gotabaya Rajapaksa resigned amidst the ongoing economic and political crises and Ranil Wickremesinghe was elected as his successor by Parliament.

[34] On 23 September 2024, following Wickremesinghe's defeat in the presidential elections and the inauguration of his successor, Anura Kumara Dissanayake, Gunawardena resigned from the position of prime minister.