After completing his education, he worked as a recording engineer, arranger and programmer, before beginning to produce independent music and compose for films.

[8] Sify wrote that the gaana songs were "one of the major highlight of the film"[9] and Behindwoods called the Attakathi album an "experimental yet fresh attempt".

[10] Following Attakathi, he composed the music for the films Uyir Mozhi and Pizza, the directorial debuts of Raja and Karthik Subbaraj, respectively.

[27] The score received equal praise with Baradwaj Rangan terming it as "great",[28] IANS as "life-affirming",[29] Rediff as "sensational"[30] and Sify as "outstanding".

[33] The soundtrack and score featured a melange and fusion of several genres, including Gangsta rap, folk, electro.

[33] His work was well received again; while The Times of India, in its album review, wrote that "Santhosh Narayanan shows, yet again, that he is one of those composers to watch out for — both for his new sounds and tunes",[34] The Hindu's Baradwaj Rangan stated that "his flamboyant score imbues even the weaker scenes with a Tarantinoesque swagger".

[36] The soundtrack to Enakkul Oruvan, the Tamil remake of the Kannada film Lucia, for which he had composed the score, was his final 2014 release.

[39] Upcoming projects of Santhosh Narayanan include the next films of directors Karthik Subbaraj and Nalan Kumarasamy.

[40] In 2016, he composed songs for Sudha Kongara's bilingual sports drama Irudhi Suttru(filmed simultaneously in Hindi as Saala Khadoos).

Six releases during the year including music compositions for Iruthi Suttru, Manithan, Kadhalum Kadanthu Pogum, Iraivi, Kabali, Kaashmora, Kodi.

In 2018 he gave scored Karthik Subbarraj's silent thriller film Mercury and Vetrimaaran's Vada Chennai, the latter being Santhosh's 25th as a composer.

According to Santhosh, he said that "the film is influenced by the aspects of Madras, as it is mostly about the descriptive and realistic portrayal of North Chennai, while the boxing culture during the 1970s also serve as the subplot".