After graduating from Sarvajana High School, Coimbatore in 1984, Thennavan moved to Chennai to pursue a career in films.
Thennavan made his acting debut in Bharathiraja's 1990 film En Uyir Thozhan, portraying a secondary lead role.
Playing a sidekick to Vikram's titular character, The Hindu gave him a positive review writing "he does a convincing job" and "his penetrating stare takes care of the expressions.
[4] Thennavan then played the lead role in an experimental film, Ayul Regai (2005), winning critical acclaim for his portrayal of a man on the verge of depression.
A critic praised his contribution to the film, noting with "a wiry frame, unkempt hair and large eyes, he fits the role perfectly.