The pair have reportedly declined repeated offers from filmmakers wishing to cast them together, following turmoil suffered by both families after Kareena's sister Karisma broke off her engagement to Abhishek Bachchan.
A source close to the film told The Times of India: "In Satyagrah Kareena plays Ajay Devgn's ladylove and Amitabhji his mentor.
"Kareena's character has strong views on politics and when she realises Devgn is going astray, stands up against him and his teacher."
"She will share an interactive space with Bachchanji's character that will lend her immense power. After Madhuri Dixit in Mrityudand, Kareena in Satyagrah is perhaps the director's second-strongest leading lady," added the source.
The actors were last seen in Govind Nihalani's Dev in 2004, though they did not share a single scene.
Kareena and Abhishek also considered working together for Players after years of estrangement.
Watch a Kareena Kapoor song from Dev below: