

His other popular songs include "Ava Enna" from the Vaaranam Aayiram (2009), the title track from Unnale Unnale, "Behka" from Ghajini. His songs for Telugu films for Kotha Bangaru Lokam (Nijanga Nenenaa), Happy Days (Arare Arare, Oh My Friend), "Badhulu Tochanai" ( Mr.Perfect), "Manase Guvvai" ( Naa Peru Shiva), "Oh Oh My Friend" ( Oh My Friend), "Yedhuta nlichindhi choodu" ( Vaana), "Meghama" ( Journey), "Yevvaro" ( Bodyguard) are very popular. "Ennaku Oru Girlfriend" from the Tamil film Boys was one of the biggest hits of the year as was "Oru Maalai" ( Ghajini 2005). Rahman, Ilaiyaraaja, Hamsalekha, Vidyasagar, Devi Sri Prasad, Harris Jayaraj and Manisharma, in several languages – Tamil, Kannada, Telugu, Malayalam and Hindi. Karthik has sung a number of songs for many popular music directors, including A. Soon after, Rahman asked him to sing the song "Nendhukittaen" from the film Star. Rahman wanted a high-pitched alap and he eventually chose Karthik to sing the alap. Having spent over a year being a backing vocalist, Karthik got his break during the Rahman's scoring of One 2 Ka 4. Karthik eventually got the opportunity and recorded for the song.

One year later, Srinivas recommended Karthik's name to Rahman, who needed fresh voices for backing vocalists for a song from Pukar. Srinivas encouraged Karthik to look at singing as a career, which prompted Karthik to resume his singing lessons. Playback singer Srinivas, who collaborated often with Rahman was Karthik's close friend's cousin. Rahman, Karthik's dream was to meet Rahman and sing for him. He was part of a college band and regularly participated in IIT Madras Fest Saarang. He is a trained Carnatic music vocalist and has been training since his school days. Karthik developed an interest in music, early in his life.
