He was the Sri Lanka Freedom Party's chief organiser for Matara beginning in 1983, the party's Assistant Secretary and Coordinating Secretary of the Mother’s Front. He first entered the Parliament of Sri Lanka as a representative of the Matara District in 1989, and he was appointed as Minister of Post and Telecommunications in the cabinet of President Chandrika Bandaranaike Kumaratunga in 1994. He also served as the Minister of Urban Development, Construction and Public Utilities in the same Cabinet after a reshuffle and was later given the Deputy Minister of Finance portfolio. Following the election defeat of his party in 2001, he was made the Chief Opposition Whip and the Treasurer of the Sri Lanka Freedom Party. In 2004 he became the Minister of Ports, Aviation and Media in the new cabinet of President Chandrika Bandaranaike Kumaratunga. In June 2005, after conflicts with Kumaratunga, he dropped the Media Ministry, but remained Cabinet Minister of Ports and Aviation. He became the campaign manager for Presidential candidate and Prime Minister Mahinda Rajapakse. When Rajapakse won and took office in November 2005, he surprised many by appointing Samaraweera to the additional post of Foreign Minister instead of Prime Minister; Samaraweera maintained his other posts. In late January 2007, Samaraweera was replaced as Foreign Minister, but remained as Minister of Ports and Aviation. On 9 February 2007, he was sacked from the cabinet together with ministers Anura Bandaranaike and Sripathi Sooriyarachchi after falling out with the president. He then went on to create a new political party, the SLFP wing. In October 2013, the Matara Magistrate's Court issued a Court order to arrest him and 10 others for their alleged involvement in obstructing a peaceful protest march in Matara by UNP activists, to oust its leader Ranil Wickramasinghe. On 12 January 2015 Samaraweera was again appointed as Minister of Foreign Affairs under newly elected President Maithripala Sirisena. After the 2019 Presidential election, Samaraweera joined the newly form Samagi Jana Balawegaya which was launched in 2020 and led by opposition leaderSajith Premadasa. He resigned from the position of Finance minister as of 17 November 2019 even hours prior to release of the general election results. In June 2020, he announced that he would not contest at the upcoming 2020 parliamentary election which is scheduled to be held on 5 August 2020 and urged the public to not vote for his preferential number and revealed that it will be impossible to remove his name from nomination list. On 9 June 2020, he also announced that he will step back and quit parliamentary politics.
Controversies
In 2019, while being the finance minister he was accused of spreading hate speech and racist comments about Buddhism and monks urged immediate action against him for his comments about Buddhism. He also criticised honorable Cardinal Malcolm Ranjith in 2018 for Cardinal's comments on human rights and in 2019 Mangala blamed Cardinal for visiting a Buddhist monk who was fasting. He was accused of using Sri Lanka Transport Board buses to transport and locate voters for the 2019 Presidential election during his tenure as finance minister.
Personal life
He is openly homosexual. In November 2018, after homophobic comments made by President Maithripala Sirisena, he wrote on Twitter that “I would rather be a butterfly than a leech Mr. President!!!”
