He became interested in acting from a young age, first appearing as Joseph in a nativity play, and completed his studies at Stanes Anglo Indian Higher Secondary School before doing a degree in Mechanical Engineering.
Sashi Kumar became acquainted with cinematographer Sakthi Saravanan and director Raja Pandi and through them began portraying small roles in Tamil television serials.
[3] Impressed by his performance, Sashi Kumar went on to work over thirty more times with Balu Mahendra for episodes of Kadhai Neram, including for the serial's Hindi version.
Balu Mahendra then recommended Sashikumar to director Mani Ratnam during a chance meeting at Vijay Adhiraj's wedding, and the film-maker chose him to portray a LTTE separatist in the war drama, Kannathil Muthamittal (2002).
Following the release of the S. J. Surya-starrer Newtonin Moondram Vidhi (2009), Sashikumar struggled to gain film offers and considered leaving back to his home town.