Kajal's first release of 2015 was in the Telugu action film Temper, directed by Puri Jagannadh, alongside NTR Jr. The film received positive responses from critics and was a commercial success at the box office. Kajal played the role of an animal lover and on her performance, a critic from The Times of India said: "Despite her limited role, the actress does well".
Kajal at South Filmfare Awards, 2015
Next, she featured in two Tamil films, working with industry-leading actors and directors. In July, 2015 she was seen as an entrepreneur in Balaji Mohan's gangster comedy film Maari, opposite Dhanush. Critics rated it as a "regular masala movie" and Rediff noted: "Kajal Aggarwal does have a significant role to play, but their onscreen chemistry just does not work". The film became an economic success. Her other release, Suseenthiran's action film Paayum Puli, alongside Vishal, received mixed reviews and failed at the box office. Reviewers criticized her character stating: "badly written and has nothing more to do with the script" She also did a cameo appearance in the bilingual romantic comedy film Size Zero.
The year 2016 saw Kajal appear in two high-profile Telugu films. She played the lead female role, marking her first collaboration with Pawan Kalyan in the masala film Sardaar Gabbar Singh, directed by K. S. Ravindra. Critical reaction on the film was mixed to negative, though Kajal's performance was positive. A reviewer from the Deccan Chronicle wrote: "Kajal Aggarwal plays the perfect princess and looks beautiful and elegant. In fact, she is a breath of air in the film". The film grossed ₹90 crore (US$14 million) worldwide. Her second Telugu release was Srikanth Addala's family drama Brahmotsavam, opposite Mahesh Babu, it was a major critical and commercial failure. Among the female leads, her performance as a "new age girl" was well received, despite the role having a limited screen time. She next starred opposite Randeep Hooda in the romantic drama Hindi film Do Lafzon Ki Kahani. The film received moderate reviews.
In April 2016, she signed another Telugu film directed by Teja, starring opposite Rana Daggubati. In June 2016 she signed for Vivegam, starring opposite Ajith Kumar. In July 2016, she signed for the Telugu film Khaidi No. 150, starring opposite Chiranjeevi for the first time in his 150th film.
In late July 2016, she signed to perform her first item number in Koratala Siva's Janatha Garage, featuring Mohanlal, Jr NTR, Samantha Ruth Prabhu and Nithya Menen in the lead roles. The shooting of the song took place in mid-August 2016. That song, titled "Pakka Local", was well received by the audience. Her next release, Kavalai Vendam, received mixed to positive reviews, but her performance was praised by critics. In December 2016, she signed for Vijay 61, starring opposite Vijay.
Aggarwal's first 2017 release was the Telugu-language action drama film Khaidi No. 150, starring opposite Chiranjeevi. It received mostly positive reviews and turned out to be a blockbuster. Aggarwal's performance, though limited, was praised by critics. In January 2017, in a poll conducted by the Hyderabad Times, she topped the list of Most Desirable Women 2016.  In 2017, she appeared in the Political drama Nene Raju Nene Mantri, as Radha Jogendhra, a loyal wife who acts as a morale balance to Rana Daggubati's character. Her performance received huge applause from both audience and critics. She then appeared in Spy action film, Vivegam, as Yazhini Kumar, a music teacher and loving wife of a spy. Though her role is limited, her performance brought raves from critics. She then portrayed the lead female role in Atlee's Mersal as a doctor, and featured alongside Vijay for the third time in her career and her performance received positive reviews and the movie became one of the highest grossing Tamil film of 2017 and was a blockbuster. Mersal went on to join the ₹200 crore club