After graduating, Rajasekhar found work as an assistant cinematographer, working under Rajiv Menon for about nine years in many advertisement films.
Feature film
Rajasekhar's debut was in 2001, with the romantic drama Minnale. The camerawork of the advertisement films impressed his former colleague and frequent collaborator, Gautham Vasudev Menon. The film was well received and became extremely popular amongst the youth. Subsequently, Rajasekhar and Gautham vasudev menon teamed up again for the crime thriller, Kaakha Kaakha (2003). It was highly praised for its unique style of visuals and scenic views through the lens, which Rajasekhar achieved through a process known as Bleach bypass, where the silver is retained in the print, creating a washed-outlook that reflected in films. He followed it up with the remake of Kaakha Kaakha, Gharshana (2004), and Manmadhan (2004), which were received well amongst the audience.
In 2005, Rajasekhar began his collaboration with A. R. Murugadoss, which started with Ghajini. It earned him huge recognition and awards for the cinematography. Rajasekhar spent two months fine-tuning the look and de-saturating the overall images. It won him the Best Cinematographer award at the Tamil Nadu State Film Awards in 2005 and was nominated for the Best Cinematographer award in Filmfare Awards South, in 2006.
He made his Malayalam debut with 4 the People (2004). He reunited with A. R. Murugadoss for Akira (2016), the remake of Mouna Guru, having previously worked on Ghajini.
