Amirthalingam joined the newly formed
Illankai Tamil Arasu Kachchi (Federal Party) in 1949 and became leader of its Youth Front. He was ITAK's candidate for
Vaddukoddai at the
1952 parliamentary election but failed to get elected. He stood again at the
1956 parliamentary election. He was won this time and entered
Parliament. He was re-elected at the
March 1960,
July 1960 and
1965 parliamentary elections. He stood for re-election in Vaddukoddai at the
1970 parliamentary election but was defeated by the
All Ceylon Tamil Congress candidate. In 1972 the ITAK, ACTC and others formed the
Tamil United Front (later renamed
Tamil United Liberation Front). Amirthalingam was delivering leaflets along with other leading Tamil politicians (
M. Sivasithamparam,
V. N. Navaratnam,
K. P. Ratnam and
K. Thurairatnam) in 1976 when they were all arrested on government orders. Sivasithamparam was released but the others were taken to Colombo and tried for
sedition. All the defendants were acquitted after a famous
trial at bar case in which 72 Tamil lawyers including
S. J. V. Chelvanayakam and
G. G. Ponnambalam acted for the defence. S. J. V. Chelvanayakam, leader of the TULF and ITAK, died in April 1977. Amirthalingam took on the leadership of both organisations. Amirthalingam was the TULF's candidate for
Kankesanthurai at the
1977 parliamentary election. He won the election and re-entered Parliament. The TULF became the largest opposition party in Parliament and Amirthalingam became
Leader of the Opposition. Amirthalingam and all other TULF MPs boycotted Parliament from the middle of 1983 for a number of reasons: they were under pressure from
Sri Lankan Tamil militants not to stay in Parliament beyond their normal six-year term; the Sixth Amendment to the
Constitution of Sri Lanka required them to swear an oath unconditionally renouncing support for a
separate state; and the
Black July riots in which up to 3,000 Tamils were murdered by
Sinhalese mobs. After three months of absence, Amirthalingam forfeited his seat in Parliament on 22 October 1983. Amirthalingam and his family, like many families of leading Tamil politicians, fled to
Madras (now Chennai), in the Indian state of
Tamil Nadu. Whilst in India Amirthalingam took part in numerous peace talks. After the signing of the
Indo-Sri Lanka Accord in 1987 Amirthalingam returned to Sri Lanka. Amirthalingam and his wife moved into a house on Bullers Road (Baudhaloka Mawatha) in the
Cinnamon Gardens area of
Colombo. The house was shared with other leading TULF politicians (
M. Sivasithamparam,
V. Yogeswaran and
Mavai Senathirajah) and their families. Amirthalingam was one of the TULF's candidates in
Batticaloa District at the
1989 parliamentary election but failed to get elected. He was however appointed as a
National List Member of Parliament for the TULF after the election. ==Assassination==