Ajantha Ranasinghe was born on 30 May 1940 in Thalammahara, a small village in the Kurunegala district. After obtaining his primary education at the Pannala Government School, he moved to Colombo and resumed his studies at St. John's College, Nugegoda. He left after completing the GCE Ordinary Level Exams.
Ranasinghe was married to daughter of late singer Kokiladevi Weeratunga, Sarojini Weeratunge.
Ranasinghe's uncle Asoka Pieris was a well known dramatist, and he came under his influence and through that got to showcase his talent over the airwaves. At a very young age, Ranasinghe wrote Buddhist songs to the Lama Mandapaya, a program on Radio Ceylon hosted by Karunaratne Abeysekera. He participated in another program, Radio Magazine, organised by the filmmaker K. A. W. Perera. His first published work, Thivanka Rekha, a poetry collection, came out in 1964.
He wrote poetry and short stories for the children's pages of Silumina and Peramuna. His poetry was frequently published in Silumina, Vanitha Viththi, and Lankadeepa. Eventually he was selected as a staff reporter at Dinamina. He would graduate from and to the posts of Sub Editor, Local News Editor, Additional Chief Sub Editor, Chief Sub Editor, Features Editor, and Chief Editor of Navayugaya.
After three decades in journalism, Ranasinghe began writing lyrics for popular singers.[3] His verses became highly popular among the public. Award after award followed, from the Sarasaviya, OCIC, State Literary, Raigam, Sumathi, and Kumaratunga Munidasa ceremonies. In addition to being a lyricist, Ranasinghe was also a B Grade Radio Ceylon singer.