Karthik has begun his professional career as a back vocalist. Soonafter, he became one of the most promising singers in the Tamil industry. He has sung in multiple languages including Telugu( over 500 songs), Kannada( over 300 songs), Tamil( over 1000 songs) and in other languages like Malayalam,Bengali and Hindi. He is known for his versatility in the industry which gave him opportunity to sing a variety of songs. He is a trained Carnatic music vocalist and has been training since his school days under Prabha Lakshmi, Padma Krishnan and Sriram Parasuram. He was part of a college band and regularly participated in IIT Madras Fest Saarang. An ardent fan of A. R. Rahman, Karthik's dream was to meet Rahman and sing for him. Playback singer Srinivas, who collaborated often with Rahman was Karthik's close friend's cousin. Srinivas encouraged Karthik to look at singing as a career, which prompted Karthik to resume his singing lessons. One year later, Srinivas recommended Karthik's name to Rahman, who needed fresh voices for backing vocalists for a song from Pukar. Karthik eventually got the opportunity and recorded for the song. Having spent over a year being a backing vocalist, Karthik got his break during the re-recording of One 2 Ka 4. Karthik has sung a number of songs for many popular music directors, including A. R. Rahman, Ilaiyaraaja, Hamsalekha, Vidyasagar, Yuvan Shankar Raja, Harris Jeyaraj and Manisharma. He has also composed music for Vasanthabalan's period film Aravaan and Srinivas Raga's Okkadine and many advertisements. Karthik has sung over 5000 songs in Telugu, Kannada, Tamil, Malayalam and Hindi.