Balaji was born on 20 June 1985, and was raised in Chennai. He has four siblings, one younger brother, three younger sisters. He said that his father abandoned his family at an unspecified point. Balaji said in a 2013 interview with The Hindu that he changed 24 houses and 11 schools while growing up in Chennai, because his "mother just cannot stay in one place. She would move from Perambur to Thiruvanmiyur to Mylapore... no place close to each other." He failed in the twelfth grade once, while his friends passed. Before the news of his failure could spread in his neighbourhood, Balaji and his family shifted to another locality; he saw this failure as a "disaster". Balaji roamed around in random company and even assisted his friend, an AC mechanic, to keep himself occupied. Balaji eventually passed in the twelfth grade, and when he was in college, he realised that his strength was in interaction, and that the attention and acclaim he received in his college culturals gave him confidence and he realised that he had to be in the media.

After completing his B.Sc computer science from the Kumararani Meena Muthiah College of Arts in 2006, Balaji joined the Amrita School of Communication in Coimbatore for a Postgraduate Diploma in Journalism, because he wanted to become like his cousin who worked at NDTV, but when he was asked to write a report on his hostel's canteen, the 56-word report contained 47 grammatical errors, and he soon realised that English journalism was not what he was interested in. At that time he saw a newspaper advertisement of a radio station (Radio Mirchi Coimbatore) that auditioned for radio jockeys and he applied for it, though he "never knew what an RJ was back then". He said that he almost did not get selected then when he sang a gaana but was finally selected in November 2006. He has not completed his journalism course since.

In December 2011, Balaji participated in "Namma Ooru Website Creation Competition", an initiative jointly organised by IIT Madras' Rural Technology and Business Incubator and the National Internet Exchange of India to disseminate village-specific information and create an identity for villages. In March 2014, he claimed to have been a presenter at Sangarsh, an annual charity concert that raises money for people suffering from various diseases. The same month, he gave an intro in "The Madras Song", a tribute to the 375th anniversary of Chennai, formerly known as Madras.

In December 2012, Balaji discontinued Cross Talk, in response to the death of Jacintha Saldanha. In November 2013, he decided to stop the segment 120 Rs. on his show where he reviewed Tamil films, after he had been severely criticised by actors and producers from the Tamil film industry. A few months before, he had also been threatened by an employee from UTV Motion Pictures for his review of Settai. Via Twitter, he announced, "I am a normal guy who wants to do good work everyday and go home happy. I can't really handle aftermath of every show on films. After a lot of thought, I have decided not to speak about films until there's tolerance and maturity among certain people from film fraternity, which is most unlikely to happen. So, '120 show' is no more". He further stated, "I don't want to keep taking my work home. I have a one-and-half-year-old child and my wife is concerned about the phone calls I keep getting". As of July 2014, the show still runs, where he only reviews Hindi and English-language films. In July 2013, Balaji said that he would try remaining a radio jockey for at least 15 years, which he believes "no one has done in Chennai", and reiterated this in November 2015.

Balaji describes "nonsense humour and nonstop talking" as his USP. He also describes conversation as his strength, and states that his humour comes out of talking to people. Although he frequently talks about films on the radio, he never entertains gossip on the personal life of actors, due to his lack of interest in the same. He is notorious for his attacks on the English language and his jocular criticism of Tamil films, but popular for his irreverent sense of unique humour. According to Photographer Bhargavii Mani of The Hindu, the frequent echoing of the words "Ada" and "Cha" on Balaji's radio shows make them "exciting". Although known to be vivacious, loud and funny in the media, Balaji has also maintained a "rather soft-spoken, shy" personality. In a 2013 interview, Balaji said that he inherited his sense of humour from his mother, who he called "the funniest person I know ... I have only 10 per cent of her comic ability".

In November 2014, Balaji created "Panjumittai Productions", a YouTube channel where he uploads short videos dealing with contemporary issues. The first video uploaded to the channel is "Kai Phone Video 01: RJ Balaji’s Biriyani!!!", featuring Balaji distributing parcels of biryani to impoverished people on the road. The second, "Kai Phone Video 02: RJ Balaji’s 501 Views Success Party!!!", is a satire on the "success parties" that production companies host to celebrate the apparent box office success of their films. The third video, subtitled "RJ Balaji Abusing Sachin Tendulkar..!", has nothing to do with Sachin Tendulkar, but instead features Balaji asking the viewers to spread word so that a heart transplant patient named Kavya could get a heart donor. The video was deliberately titled misleadingly so that the message would spread sooner. On 12 December, less than two weeks after Balaji uploaded the video, Kavya successfully got a donor.

Balaji was married at the age of 21 years, and has a son named Mahanth who, as of 2015, is three years old. During the filming of Kadavul Irukkan Kumaru, Balaji and G. V. Prakash Kumar were involved in a major car accident near Tindivanam, but sustained only minor injuries. Although known to actively perform social services, Balaji does not consider himself a social worker or disaster manager: "I am just someone who wants to help people, and I will just do that." He has always believed in only one thing: "To be good and do good work rather than be famous. So whatever I am doing, be it professionally or working for a cause, I intend to do my best."