Gunasekaran was first elected to the Tamil Nadu Legislative Assembly as a CPI candidate from the Sivaganga constituency in the 2006 elections. This was despite complications caused by a rebel Indian National Congress politician, V. Rajasekaran, who stood as an independent when his party chose to ally with the CPI in the constituency rather than field its own candidate. Rajasekaran gained significant support from other disaffected INC members during the campaign but Gunasekaran had support from the Dravida Munnetra Kazhagam (DMK).
With support from the All India Anna Dravida Munnetra Kazhagam (AIADMK), Gunasekaran was re-elected from the Sivaganga constituency in the next elections, in 2011. However, both the AIADMK and DMK fielded candidates in the 2016 elections, when Gunasekaran lost the seat to G. Baskaran of the AIADMK. On that occasion, he was the CPI candidate in an alliance involving support from the People's Welfare Front, the Tamil Maanila Congress and the Desiya Murpokku Dravida Kazhagam.
- "Thiru. S. Gunasekaran (CPI)". Legislative Assembly of Tamil Nadu. Retrieved 2017-05-03.
- 2006 Tamil Nadu Election Results, Election Commission of India
- "MDMK has an edge over CPI in Sivaganga constituency". The Hindu. 4 May 2006. Retrieved 2017-05-03.
- Scott, D. J. Walter (12 May 2016). "Land known for its valour is in squalor". The Hindu. Retrieved 2017-05-03.
- "List of MLAs from Tamil Nadu 2011" (PDF). Government of Tamil Nadu. Retrieved 2017-05-03.
- "Sivaganga (Tamil Nadu) Election Results". Infobase. Retrieved 2017-05-03.
- "MLA stages fast protesting officials' 'non-cooperation'". India.com. PTI. 13 April 2017. Retrieved 2017-05-03.