The success of the film provided an opportunity to feature in Mani Ratnam's multi-starrer Aayutha Ezhuthu (2004), before he branched off to receive critical and commercial acclaim in Telugu and Hindi cinema through Nuvvostanante Nenoddantana (2005), Rang De Basanti and Bommarillu (2006).

[4] He noted that he knew he was headed for a career in films since childhood, showing particular fascination for writing and directing, and thus only signed up for business school as a "safety cushion" as insisted upon by his father.

[3] 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.

The script writer of that film, Sujatha, was insistent that Siddharth audition for Shankar's ongoing project Boys (2003), where the director had hoped to cast new actors.

[7][8] Siddharth shot for the film in 2002 alongside fellow debutants Genelia D'Souza, Bharath, Nakul, Thaman and Manikandan, while also suffering an injury which led to him being hospitalised for three days.

[9] The story centred on six youngsters, conveying a message about the importance of a good education and career over other distractions, such as romance and sex, and marked a move away from Shankar's usual brand of vigilante films, gaining much hype and publicity prior to release.

[11][12] Before the release of Boys, Siddharth signed on to feature in his mentor Mani Ratnam's political drama film, Aayutha Ezhuthu (2004) where he played the student Arjun Balakrishnan, a role which he described was similar to his real life persona.

Featuring in an ensemble cast including Madhavan, Suriya and Trisha, Siddharth revealed that the sync sound method of filming that the team had employed, worked in his favour, as he was able to draw experience from his stage performances.

"[13][14] Siddharth then ventured into Telugu cinema by signing on to appear in the directorial debut of Prabhu Deva, the romantic drama Nuvvostanante Nenoddantana (2005), in which he was again paired alongside Trisha.

A reviewer from Idlebrain.com noted Siddharth is "the surprise package" of the film, adding "he epitomized the essence of his character and won the hearts of audiences with his zest portrayal of mischievous yet lovable guy".

[20] He then wrote the story and worked on the screenplay for his next release, the Telugu film Chukkallo Chandrudu (2006) directed by Sivakumar, also being credited as a playback singer for the first time.

[21] Described as a "sophisticated comedy film for multiplex crowds", it opened to mixed reviews with Siddharth's contribution described as a "redeeming factor", but failed at the box office.

Cast opposite Genelia for the second time, Bhaskar revealed he chose Siddharth to play the lead role because of his similarities in body language with the character.

During the shoot, the director praised the actor's versatility and dedication to the role, adding he was "mesmerised" after Siddharth performed a scene close to four minutes without a cut.

[39] Anand Ranga's Oye!, saw Siddharth appear in another role as a romantic hero and paired opposite actress Shamili, while he also contributed as the film's soundtrack album producer working with Yuvan Shankar Raja.

[40] The film opened to mixed reviews and had an average run at the box office, with a critic noting "Siddharth has given a brilliant performance as a lover boy, but his acting is not up to the mark in some emotional scenes".

Siddharth became extensively involved with the making of the film and in order to adapt into the role, he took training in the sport for two months and relocated to the Malwani district in Mumbai.

[49] The actor was then selected to portray the lead role of a blind warrior in Prakash Kovelamudi's fantasy epic Anaganaga O Dheerudu co-produced by Walt Disney Pictures and veteran director K. Raghavendra Rao.

Beginning production in June 2009, it became the actor's most expensive film till date and marked the debuts of actresses Shruti Haasan and Lakshmi Manchu in Telugu cinema.

The venture marked his return to Tamil films after a seven-year hiatus, and he was seen portraying a doctor who flees from his American life to begin fresh in India.

[54][55] His third release of the year was the romantic college drama, Oh My Friend co-starring Shruti Haasan and Hansika Motwani, which opened to mixed reviews but proved to be a commercial success at the box office.

He financed the college romantic comedy Kadhalil Sodhappuvadhu Yeppadi (2012), based on the same-titled short film by Balaji Mohan, and featured in the lead role alongside Amala Paul.

Siddharth was selected to be a part of the ensemble cast for Deepa Mehta's Midnight's Children, a 2012 British-Canadian film adaptation of Salman Rushdie's 1981 novel of the same name.

[65] He then featured in Sundar C's commercially successful Tamil comedy film Theeya Velai Seiyyanum Kumaru portraying a timid IT employee who seeks the help of a love guru.

[67] By early 2014, Siddharth worked simultaneously on three Tamil projects claiming in an interview to The Hindu newspaper that the year was likely to "be a turning point in his career".

[75] Working alongside Prithviraj and Vedhika, he portrayed the leading role of Thalaivankottai "Kaali"appa Bhagavathar, a Madras theatre artiste, loosely based on the life of actor S. G. Kittappa.

To prepare for the role, he studied the work of actors from the 1920s and made himself familiar with the lives of artistes from that time period, noting his stint in theatre was helpful.

[82] After a six-month sabbatical, Siddharth announced that he had finished work on another acting and production venture, Jil Jung Juk by newcomer Deeraj Vaidy.

As he actively worked in both Hindi and South Indian film industry, Parle Agro signed him as a nation-wide brand ambassador in 2012 owing to his pan-Indian appeal.