Karthik Raja is the eldest son of musician Mastro Ilaiyaraaja. His brother Yuvan Shankar Raja and sister Bhavatharini, who are also Tamil film music directors and playback singers, have worked with him on notable projects. He did his schooling at St. Bede's School in Chennai and graduated from Loyola College, Chennai. He married Raja Rajeswari at Tirupati on 8 June 2000. He had his formal training in Western classical music from the Trinity School of Music, mainly in piano (affiliated with Jacob John). He also had training in Carnatic music from T. V. Gopalakrishnan and Malayalam composer V. Dakshinamoorthy. At the age of 13, Karthik Raja played the keyboard for the song Kannukkum from the Tamil movie Ninaikka Therinda Maname in 1987. Many such outings followed including playing keyboard for the soundtrack of the movie Nayagan. Karthik also arranged many recordings for his father and composed his first song "Pandianin Rajiyathil" for the movie Pandiyan and "Ninaikindra" for the movie Athma. Around this time, he also composed some background scores for the TV series Bible. He debuted as a full-fledged composer in 1996 through the Tamil movie Alexander, soon followed by Manikyam. Then came many chart-busters that included Ullaasam, Naam Iruvar Nammaku Iruvar, Kadhala Kadhala and Dumm Dumm Dumm among others. He also debuted in Hindi films with Grahan which won him the R.D. Burman award for the best new talent.