He made his breakthrough by playing the lead role in Madha Yaanai Koottam (2013)[1][2] and gained critical acclaim for his performance in Kirumi (2015), Vikram Vedha (2017), Pariyerum Perumal (2018) and Sigai (2019).

[6][7][8] Kathir then won critical acclaim for his performance in the thriller film, Kirumi (2015) directed by Anucharan and written by Manikandan.

[9][10] The film was also sent to international film festivals, with a critic from The Hollywood Reporter noting that "playing his namesake character, Kathir makes for a particularly avid small-time crook, effortlessly cataloging useful information for the police officers he smoothly ingratiates himself with by dint of feigned respect and subtle manipulation".

He was also cast in Vikram Vedha with R. Madhavan and Vijay Sethupathi, Pa. Ranjith's production Pariyerum Perumal (2018), for which he attained national acclaim and was noted for his "outstanding performance".

[16] Looking fresh from his Bigil football overkill, Kathir takes lead in a film that mixes entertainment, sport and horror to a confused extent.