Janaki was born on April 23, 1938 in Palapatla, Repalle Taluk, in Guntur District of Andhra Pradesh. She was a child prodigy who took to singing at a tender age of three, kindled by music programs on radio. She was taught her early music lessons by Sree Paidiswamy at Rajamundhry, until she was ten.

Her father-in-law, a music artiste, who was nicknamed “fun doctor” Chandrasekharam, recognized her penchant for music and nurtured it. She learned to modulate her voice on a wide range from a three year-old to an eighty year old! She acquired a second prize from the former President of India, Dr. Rajendra Prasad in 1956, at a competition held by All India Radio. Mr. Chandrasekharam later took her to Chennai and introduced her to AVM Studios in 1957. Singer P. Suseela's contract with AVM was over and the company was looking for a new voice. At the audition test at AVM, music directors R. Sundarsanam and Govardhanam heard the young singer from Andhra Pradesh sing Lata Mangeshkar's "Rasik Balma," and was impressed. Janaki started her career as a staff singer at AVM, and got instantaneous appreciation for her charismatic voice.

Her voice is so captivating that during one of her performances, people gathered to watch a nearby film shooting joined her program. This got her the first break as a playback singer after which, she never looked back. Through the first year of her career she sang almost 100 songs in six languages, without much effort, which was a record in those days. Thereafter she kept on climbing up her career ladder.