In 2008, Sen began his career as a
film composer, with the
Hindi film Sirf, however, the film was supposed to be released in 2006, but it got delayed badly and was released in 2008 and eventually the music went unnoticed. He also composed the music for
The Murderer (2009), which also got delayed and the music went unnoticed. Initially he wanted his all-time favourite composer
A. R. Rahman to compose for the film, but Rahman couldn't do it, because he wanted to compose for Danny Boyle's
Slumdog Millionaire instead. So, he started looking for someone who is capable and can contribute all his time for composing in his film alone. Sen was always keen to work with Ashutosh Gowariker and incidentally his father Sameer Sen knew him from before and knowing that Gowariker was looking for someone to compose for his film, Sen asked his father to fix a meeting with him. His first meeting with Gowariker was a casual one at his office, it was where he told him that he would like to make him listen to some of his compositions. Gowariker immediately agreed to visit his studio the next morning. The next day, when he went to Sen's studio and heard some of his tunes, he really liked what he heard and after a couple of weeks later, Gowariker called up Sen and said "You are on for this project". For Sen, it was a dream come true. At first Sen was thrilled of getting the offer, but when he was told that there would be 13 songs in the movie, one song for each of the 12 zodiac signs and then one song in which the lead protagonist makes the final choice, he was taken aback, since nowadays its quite rare to hear 13 different songs in one album and that itself was a difficult task, and again, it was an equally difficult task to create 13 distinct songs, each for one particular zodiac sign and then incorporating the flavor of all these 12 songs into that final song, was the most toughest task, however he took it up as a challenge and started working on the music, which took more than one and a half years in the making. The
soundtrack of the film, was released in August 2009 and irrespective of the box office status of the film, it has been able to garner mostly positive critical responses.
BBC Music praised Sen's work and quoted him as "Sen shows he can successfully compete with the best in Bollywood".{{cite web|author=Verma, Sukanya|title=Khelein Hum... has beautiful music In 2011, he has had a major release with a top banner
Yash Raj Films –
Mere Brother Ki Dulhan, the music of which got appreciation from both critics and masses. The songs "Dhunki", "Isq Risk" and title track were chartbusters. In 2012, he replaced
Pritam as the music director for
Salman Khan's next film
Ek Tha Tiger, since Pritam had date problems with both Yash Raj projects
Ek Tha Tiger and
Dhoom 3.{{cite web|title=Pritam chooses Dhoom 3 over Ek Tha Tiger|url=http://www.bollywoodhungama.com/features/2011/09/15/7919/index.html ==Discography==