He has sung more than 8000 songs in 10 Indian languages including Tamil, Telugu, Malayalam, Kannada, Odia, Bengali, Marathi and Hindi.

One year later, Srinivas recommended Karthik's name to Rahman, who needed fresh voices for backing vocalists for a song from Pukar.

Karthik has sung a number of songs for many popular music directors, including A. R. Rahman, Ilaiyaraaja, Hamsalekha, Vidyasagar, Devi Sri Prasad, Harris Jayaraj and Manisharma, in several languages – Tamil, Telugu, Kannada, Malayalam and Hindi.

Karthik has sung Kannada songs and has many super hit chart buster songs to his credit like Ale Ale, Anuraaga Aralo Samaya, Thangaliyalli Theli Hode, Nee Chummu Chummu Munjaaneli, Manasaithu Ninna Myaale, Sum Sumne Yaako, Hosadondu Hesaridu Nanange, Kanne Koodiruvaaga, Madhumasa, Nenapidu Nenapidu, Thanthaane Thannamthaane, Baruve Odi Odi Nalidu, Raktha Sambandhagala, Saluge Saluge, Mannige Mara Bhaarave and many more.

In 2010, he sang a track "Behene De", from Hindi film Raavan, which is widely considered as the biggest song in his career.

[2] The song Yayum Ngayum from the album Sandham: Symphony Meets Classical Tamil is considered as one of Karthik's career best for the way how he has brought sensuality to the 2000 year old poetry.

He is the music director of Vasanthabalan's period film Aravaan and Srinivas Raga's Okkadine starring Nara Rohit and Nithya Menen in Telugu.

[6] He is the composer of the segment 'Guitar Kambi mele Nindru' directed by Gautham Vasudev Menon in the Netflix anthology movie Navarasa (2021).

I fully support #MeToo and if there's truth in anybody's grievance, I shall be more than willing to apologise or face legal action because I don't want to ever leave a sour taste in anyone's life".