His father Selvarajan was a singer who performed in stage shows organised by famous music directors such as Gangai Amaren, Ilayaraja, and Deva among others. Rajkumar had been a silent devotee of his father's musical career and enhanced an interest in music. It was his mother who unearthed his flair for music and convinced his father to make him go for music classes. Rajkumar was trained in classical music under the counseling of Subbaiah Bhagavathar for 3 years.
After completion of his music training, Rajkumar started to organise musical shows on his own and was in search for film opportunities. Come 1987 and director duo Robert-Rajashekar gave him his first major breakthrough by signing him as the music composer for their film Chinna Poove Mella Pesu. Since then, Rajkumar has composed music for over hundred films in Tamil, Malayalam, Telugu and Kannada language films. His compositions for the films such as Suryavamsam, Unnidathil Ennai Koduthen, Aval Varuvala, Vanathai Pola, Thulladha Manamum Thullum, Vasantham , and "Priyamaana Thozhi" have all been blockbuster musical hits and regarded memorable for long time.