Success (2009–present)

She had four releases in 2009; she first starred in another Tamil film Modhi Vilayadu, which garnered mixed reviews and was a financial failure, following which she appeared in the high-budget Telugu historical drama Magadheera, which saw her essaying double roles for the first time. The film, directed by S. S. Rajamouli, received universal critical acclaim, while Kajal, particularly, was praised for her portrayal of a princess in the film. Rediff wrote that she "was quite a surprise package, [...] sweet and charming and looked like an 'ethereal' princess. She carries off both the roles fairly well", while NDTV cited that "Kajal Agarwal is also an asset to the film. She is very apt for the character of the princess. Besides filling the glamour slot, she has proven that given a chance, she too can give an excellent performance". The film was also highly commercially successful and broke several records, emerging as the highest-grossing Telugu film of all time. Magadheera's enormous success turned Kajal into one of the most sought-after actresses in the Telugu film industry and catapulted her into the main foray of lead Telugu actresses. Her subsequent releases Ganesh Just Ganesh and Arya 2 received mixed reviews from critics, while her performance garnered positive feedback.

Kajal's first 2010 release was A. Karunakaran's Darling which featured her alongside Prabhas and received favorable response, becoming a commercial success at the box office, with Kajal receiving her second Filmfare nomination for Best Actress for her performance. In August, she appeared in the Tamil thriller film Naan Mohaan Alla opposite Karthi, which was based on a real life incident and opened to unanimously positive reviews. The film performed well at the box office and was declared a blockbuster. Kajal's final release in 2010 was Brindavanam opposite NTR Jr. and Samantha, which received critical acclaim and went on to become an economical success as well, while fetching Kajal the CineMAA Award for Best Actress. In 2011, she was paired with Prabhas for the second time in Mr. Perfect, directed by Dasaradh. The film opened to positive reviews, while Kajal won appraisal by critics with Times Of India writing, "What is applause-worthy in the movie is Kajal Agarwal's performance. She looks great, expresses well and fits into the role perfectly". In May, she appeared in Veera opposite Ravi Teja that received negative reviews. She subsequently made her Bollywood debut in a leading role with Singham, a remake of the same-titled 2010 Tamil film, opposite Ajay Devgan. The film received mixed reviews from critics, as did her portrayal of a Goan girl Kavya Bhosle, but became a "Super Hit" at the box office, collecting 85 crore (US$18.96 million) within three weeks. She is also making her debut in Kannada in Raju Hasan's Thathasthu opposite Chirag, and would play the female lead role opposite Surya in Maatraan.