Thamilselvan was born in Chavakacheri, and was originally a barber by profession
. He joined the LTTE after the 1983 Colombo riots, and received training in India whose government was then backing the Tigers. At one point, he was the personal bodyguard of the LTTE supreme leader, Vellupillai Prabhakaran. He became area commander for Jaffna during the IPKF intervention in the late 1980s. In 1993, he suffered a shrapnel wound at the Punarin Battle which left him with a permanent limp. In 2001, he narrowly avoided being killed by the Sri Lankan Army's Deep Penetration Unit. His wife serves in the women's wing of the LTTE.
Thamilselvan began to rise in the movement after the capture of Jaffna city by government forces in the late 1990s. When Norway began mediating in the peace efforts, he began to become more prominent due to the worsening health of the LTTE's international spokesman, Anton Balasingham, and led the LTTE's delegation during peace talks in Geneva.
Thamilselvan was killed by the Sri Lankan Air Force on Friday 2nd November 2007 during an aerial bombardment of Kilinochchi.