Balasubrahmanyam was born to S. P. Sambamurthy, a Harikatha artiste who had also acted in plays. He has two brothers and five sisters, including singer S.P. Sailaja. He studied notations and learned to play instruments such as the harmonium and flute on his own while listening to his father. He enrolled at JNTU College of Engineering Anantapur with the intention of becoming an engineer. He discontinued his studies early due to typhoid and joined as an Associate Member of the Institution of Engineers, Chennai. He continued to pursue music during his engineering studies and won awards at singing competitions. In 1964, he won the first prize in a music competition for amateur singers organised by the Madras-based Telugu Cultural Organisation. He was the leader of a light music troupe composed of Anirutta (on the harmonium), Ilaiyaraaja (on guitar and later on harmonium), Baskar (on percussion), and Gangai Amaran (on guitar). He first composed a music in the film Kanya Kumari in 1977. He has composed music over 50 films. He was selected as the best singer in a singing competition which was judged by S. P. Kodandapani and Ghantasala. It was rendered by veteran playback singer P. B. Srinivas, who used to write and give him multi-lingual verses in Telugu, Tamil, Hindi, Kannada, Malayalam, Sanskrit, English and Urdu. Balasubramanyam is married to Savitri and has two children, a daughter Pallavi, and a son S. P. B. Charan, also a playback singer and film producer.