Siddharth was born to a Tamil-speaking family. He began his education at DAV Boys' Senior Secondary School, Chennai and then studied at Sardar Patel Vidyalaya, Delhi. He subsequently graduated with a Bachelor of Commerce (Honors) degree from Kirori Mal College, New Delhi.
Siddharth's first tryst with media came through dubbing for the Banish mosquito repellent ad in eight different languages in 1988, as instructed by his father's close friend, ad director Jayendra. He made his singing debut in the film Chukkallo Chandrudu in 2006. He has sung over 15 songs in Tamil, Telugu and Hindi. He pursued amateur theatre during his time in Delhi through live stage performances with the theatre group Players, while also honing his writing and directorial skills. After finishing his education, he apprenticed with ad film maker Jayendra and cinematographer P. C. Sreeram, who both helped him join as an assistant director for Mani Ratnam's Kannathil Muthamittal. Siddharth shot for the film throughout 2002, the movie Boys alongside fellow debutants Genelia D'Souza, Bharath, Nakul, Thaman and Manikandan, the film opened to mixed reviews but became a moderate success at the box office. Before the release of Boys, Siddharth signed on to feature in his mentor Mani Ratnam's political drama film, Aaytha Ezhuthu. He then ventured into Telugu films by signing on to appear in Prabhu Deva's first directorial project, the romantic drama Nuvvostanante Nenoddantana. The film consequently went on to become an all-time blockbuster in the Telugu film industry, and Siddharth became a much sought after actor in Telugu films. By early 2014, his first release of the year was Karthik Subbaraj's musical gangster film Jigarthanda. The film subsequently went on to become among the most profitable Tamil films of the year. However both Kaaviya Thalaivan and Enakkul Oruvan failed commercially at the box office, prompting the actor to take a break from films. After a six-month sabbatical, Siddharth announced that he had finished work on another acting and production venture, Jill Jung Juk by newcomer Deeraj Vaidy. He has also worked on Sundar C's horror comedy, Aranmanai 2 alongside Trisha and Hansika Motwani. Furthermore, Siddharth has signed on to appear in a Malayalam film directed by ad film maker Rathish Ambat in his feature film debut.