S. Janaki was born in Pallapatla, Repalle village, Guntur District of Andhra Pradesh. Janaki showed interest in music at a tender age and started singing at the age of three. She started learning music from a nadaswaram vidwan, Sree Paidiswamy. She moved to Chennai on the advice of her uncle Dr. Chandrashekar and joined as a singer in AVM Studio and started her career with Tamil films in 1957 in the film 'Vidhiyin Vilayattu' under the music director T. Chalapati Rao. Later, she got a chance in a Telugu film MLA.
She wrote many songs for Tamil and Telugu films. She has sung many songs, in almost all languages in South India as well as in Hindi, Kannada, Sinhalese, Bengali, Oriya, English, Sanskrit, Konkani, Tulu, Saurashtra, Baduga, Japanese and German