Rajkumar was born to Selvarajan and Kannammal. His father was a vocalist performing in stage shows conducted by popular music directors such as Ilayaraja, Gangai Amaren, Deva among others. Rajkumar underwent classical music training under the guidance of Subbaiah Bhagavathar for 3 years. It was in 1987, director duo Robert-Rajashekar came forward to sign him as the music director for their film Chinna Poove Mella Pesu. This film had Prabhu and Ramki in the lead roles. Since then, Rajkumar has scored for over hundred films in Tamil, Telugu and Kannada film industries. His scores for the films such as Suryavamsam, Aval Varuvala, Unnidathil Ennai Koduthen, Thulladha Manamum Thullum, Vanathai Pola, Raja (1999 film), Vasantham , Priyamaanavale , "Priyamaana Thozhi" have all been huge hits and considered memorable for long time. Rajkumar has composed songs for many hit films in Kannada starring South Super Star Dr.Vishnuvardhan, a star of 220 movies in five different languages. The hit films in their combination includes Sirivantha, Varsha, Jyeshta and many more. The all time ever green songs of Kannada Cinema, Sevanthiye Sevanthiye sung by Indian play back singer Dr.S. P. Balasubrahmanyam, a song from the Kannada blockbuster film Surya Vamsha and Premachandrama from another blockbuster film Yejamana sung by south singer Rajesh Krishnan, was originally composed by Rajkumar. Hence, Dr.Vishnu and S.A.Rajkumar's combination has given the industry best of best compositions.