Karthik had a good interest in music early in his life and had learnt Carnatic music during his school days. Later on he started singing for his college band and regularly participated in IIT Madras Fest ‘Sarang’.
Being an ardent fan of A. R. Rahman, Karthik always dreamt of meeting the musical great. After searching a lot of avenues, he happened to find out that one of his close friend's cousin was singerSrinivas, who sang many songs for Rahman. During their brief chat, Srinivas asked Karthik to sing a few lines, and was impressed by his voice and asked him to look at singing more seriously. Taking cue, Karthik resumed his singing lessons.
After nearly a year since his meeting with Srinivas, Karthik received a call one night from him. Apparently Rahman needed a fresh voices forbacking vocalists for a song from Pukar and Srinivas could not get in touch with one of the singers and then he remembered Karthik and tried to get in touch with him. Ironically Karthik was out with his friends and was not reachable for quite some time. As luck would have it, he managed to get the information just in time and rushed to the recording studio.
Having spent over a year being a backing vocalist, Karthik got his break during the re-recording of One 2 Ka 4. For the background score of one of the scenes in the movie, A. R. Rahman wanted a high-pitched alap and Karthik along with other chorus singers gave a shot at it. Rahmanimpressed with the voice, asked him stay back for the recording. Karthik grabbed the opportunity with both hands and performed, with Rahman giving him pointers and walking through the alap. He struck gold with this session and soon Rahman asked him to perform for a song Nendhukittaen from the film Star.
Karthik has sung a number of songs for many popular music directors, including Ilayaraaja, A. R. Rahman, Yuvan Shankar Raja and Harris Jeyaraj. Karthik has sung songs in several languages – Hindi, Tamil, Telugu, Malayalam, and Kannada. Ennaku Oru Girlfriend from the Tamil movie Boys was one of his huge hits as was Oru Maalai from the 2005 film Ghajini. His recent track in 2008, the gaana inspired "Ava Enna" from the film Vaaranam Aayiram has been well received.