Samuel James Velupillai Chelvanayakam was born in Ipoh, Malaysia on 31 March 1898 to Viswanathan Velupillai, a businessman, and Harriet Annamma Kanapathipillai. He moved to Tellippallai, Sri Lanka, with his mother, two brothers, and sister (only his brother E. V. Ponnuthurai survived past childhood) in order to receive his early education at Union College, Tellipalai for eight years. From then he studied for five years at St. Johns College, Jaffna, and then to St. Thomas’s College, Mount Lavinia. Chelvanayakam graduated from the University of London as an external student in 1918 with a degree in Science. In 1927 he married Emily Grace Barr-Kumarakulasinghe. They had four sons and one daughter.
He was a teacher at St. Thomas’s College until moving to Wesley College in 1919 to teach Mathematics. He later became the Head of the Science Department. He attended lectures at the Law College and sat for the law examinations at the Law College while he was still teaching at Wesley College. Chelvanyakam started his legal career in the Court of Requests in Colombo. He set up a private practice first in Hultsdorp and later in St. Sebastian Hill. From the Court of Requests, Chelvanayakam moved to the District Court and later to the Appellate Courts. He was made Queen’s Counsel on 31st May 1947.
Chelvanayakam then left his practice and joined politics as a primary organizer of the All Ceylon Tamil Congress (ACTC) in 1944. He was elected as a member of Parliament for the first time in September 1947. On 18 December 1949, Chelvanayakam launched the Ilankai Thamil Arasu Kadchi (ITAK, also known as the Federal Party) along with E. M. V. Naganathan and V. Navaratnam elected as joint General Secretaries. He was also a director of the Tamil newspaper Suthanthiran (Freedom).
Chelvanayakam was known by Tamils as Thanthai Chelva (Father Chelva) because of his interest in safeguarding the identity and interests of Tamil people.
Together with the Prime Minister of Sri Lanka he signed the Bandaranaike-Chelvanayakam Pact on 26 July 1957 which would request parity for the Tamil language; cessation of colonization on traditional Tamil-speaking homelands; give reginal autonomy for the Tamil provinces; and restore the citizenship and rights of the upcountry Tamils (S. J. V. Chelvanayakam and the Crisis of Sri Lankan Tamil Nationalism / A. J. Wilson). On 24 March 1965 he signed the Senanayake-Chelvanayakam Pact which addressed the Tamil Language Special Provisions Act No. 28 of 1958 but this was not passed.
Chelvanayakam’s health declined due to Parkinson’s disease and in 1961 he had surgery in Edinburgh. After suffering from a fall resulting in head injuries in March 1977, Chelvanayakam passed away on 26 April 1977.