Ranjith was born in Kozhikode, Kerala. Ranjith was artistically inclined even during his school days. It was his opposition to conventional college education that landed him at School of Drama and Fine Arts. Here, he bonded with a group of artistic talents that included Alex Kadavil, at whose house in Thiruvanthapuram Ranjith stayed for a while after his education. During the late eighties, Ranjith tried his hand at skits and television serials for Doordarshan.
Renjith associated himself with the making of Oru Maymasa Pulariyil (1987), which marked his entry into Malayalam cinema. In the year 1988, Ranjith made his formal entry into the film world by writing the story for Orkkapurathu, a fun-adventure film directed by Kamal with Mohanlal in the lead. The immediate success of Orkkapurathu brought Ranjith several chances to work in films. In the late eighties and early nineties, Ranjith wrote scripts for several small budget films mainly for Kamal. Another director with whom Ranjith joined hands in those days was Viji Thampi. Despite having a series of subsequent films in his hands, and most being average hits, Ranjith could not establish himself as a successful writer.
The year 1993 was a huge turning point in Ranjith's career. Devasuram, his film based on the life of Mullassery Rajajagopal, a father-like figure to him, turned into a huge hit at the box office. With Mohanlal in the lead and directed by I. V. Sasi, Devasuram was both critically and commercially a very big success. Mohanlal's performance was highly appreciated and it opened a new genre of feudal stories in Malayalam cinema. Within two months of the release of Devasuram, his next movie, Maya Mayuram (directed by Sibi Malayil and starring Mohanlal) was released, but it did not meet its anticipated success. According to Ranjith, Maya Mayuram is one of his best films and its failure affected him greatly. Towards the end of 1997, Ranjith penned Aaraam Thampuran, one of the blockbuster hits of his career. Directed by Shaji Kailas, this film broke several collection records and went on to become a financially and critically acclaimed hit. This film was also a turning point in the career of Mohanlal. With this film, Ranjith gained a reputation as a commercially viable scriptwriter. Then came Kaikudanna Nilavu, in 1998, directed by Kamal, starring Jayaram, yet another average hit. The year 2000 began with the release of Narasimham, directed by Shaji Kailas. With Mohanlal playing the lead role, this film became one of the biggest hits ever in the history of Malayalam cinema till then. Yet again in 2000, together with Shaji Kailas, Ranjith repeated history. His Onam release Valliettan starring Mammooty became one of the biggest hits in the history. With this film, Renjith became the most successful scriptwriter of the time.
In 2001, Ranjith made his directorial debut with Ravanaprabhu, the sequel to Devasuram. With Mohanlal appearing in dual roles as father and son, this film turned out to be one of the biggest hits of Malayalam cinema. In the year 2008, Ranjith stunned Kerala with his film Thirakkatha, based on actress Srividya's life, which won the National Award for the Best Malayalam Feature Film. Starring Anoop Menon and Priyamani in the lead, the movie featured Prithviraj and Samvrutha Sunil in important supporting roles.
Ranjith also occupied in the respected position of School Director for Cochin Media School, fist authentic Film & Broadcasting Institute in Kerala. Ranjith also appeared as judge in "Mammootty the Best Actor Award — II", an acting talent hunt reality show aired in Asianet.