Mr. Sampanthan, who, in 1956, joined the Ilankai Tamil Arasu Katchi (also known as Federal Party), was first elected to Parliament from Trincomalee in 1977 on the ticket of the TULF when the general elections were held under the 1972 Constitution.

After resigning as MP along with other members of the TULF in 1983, Mr. Sampanthan returned to the Parliament in July 1997. Since 2001, he has been heading the TNA, which now comprises the ITAK, the Tamil Eelam Liberation Organisation (TELO), the Eelam People’s Revolutionary Liberation Front (EPRLF) and the People’s Liberation Organisation of Tamil Eelam (PLOTE). According to records of the Parliament, Mr. Sampanthan has served as MP for more than 22 years.

He was appointed as the Leader of the Opposition of the 8th Parliament of the Democratic Socialist Republic of Sri Lanka on the 1st of September 2015