Sivakarthikeyan became well known for his light-hearted trolls and mockery of co-hosts and participants in shows, as well as his impersonations of several film actors, especially Rajinikanth. He received further opportunities to host several shows on Star Vijay like Airtel Super Singer and Jodi Number One Season 5. He hosted the special edition of a popular talk show, Koffee with Siva, after Koffee with Anu had discontinued due to Anu Haasan's retirement. However it was his game show, Athu Ithu Ethu that made him reach a wide range of audience. He got opportunities to host promotional film events as well as the 5th and 6th editions of the Vijay Awards. He regularly appeared in short films including his friend Atlee's Mugapputhagam, Identity, Kurahl 786 and 360°, while balancing his career as a television host.

In 2013 he appeared in three commercially successful films which hits 100 days. In his first release of the year,Kedi Billa Killadi Ranga, a dual hero coming-of-age comedy, Siva Karthikeyan partnered once again with Pandiraj and shot for the film in his hometown of Tiruchirappalli alongside Vimal. The film opened to positive reviews with critics. The film became a surprise success at the box office and ended up being a profitable venture for producers and distributors, It brings out the acting skill of him. His next success was through Dhanush's debut production venture Ethir Neechal, written and directed by Durai Senthilkumar, a former assistant of film Director, Vetrimaran. It is a story about a Common Young man having talent as a Runner, who strives to make his identity into a pride one. His third release in 2013, Director Ponram's comedy Varuthapadatha Valibar Sangam, saw him portray a carefree rural youth where he paired up with another newcomer Sri Divya. Actor Soori played an important role in the film as Sivakarthikeyan's close aide. It was also the first time that Siva Karthikeyan sang a song in a film and a promotional video of its making was released to market the film. He won positive reviews for his performance from critics, with Sify noting "Sivakarthikeyan is terrific as Bosepandi because he makes this yarn look so believable on screen with his body language, eyes and dialogue delivery". Another reviewer called him a delight to watch and claimed that he carried the script. The film completed 100 days during its theatrical run and is Sivakarthikeyan's biggest commercial box office success to date. Sivakarthikeyan's entertaining performances in 2013 has led him winning the Vijay Awards 2013 for the "Entertainer of the year". "It was the memorable moment," says Siva Karthikeyan.

He started the year 2014 with a comedy film Maan Karate produced by A R Murugadoss The film featured him as a carefree urban youth who fakes himself as a boxer to impress a girl. The film was a commercial success.

In 2015, Siva Karthikeyan paired up once again with his Ethir Neechal Director, Durai Senthilkumar, for a cop film, Kakki Sattai. The film released on 27 February 2015 with positive reviews stating that Siva Karthikeyan entertains. It was a story about a sincere Constable who takes risks to protect black Organ donation and having the aim to become an Inspector. He again joined hands with his Varuthapadatha Valibar Sangam Director in the film Rajini Murugan. The film's Producer, N. Lingusamy, ultimately failed to provide Siva Karthikeyan with his salary due to losses incurred by the film's delayed release. His film Remo, directed by debutant Bakkiyaraj Kannan and produced by R. D. Raja, featured Siva Karthikeyan playing love-struck youth disguising himself as a female nurse to befriend his love interest.