In the early 18th century, the court of Maratha Chhatrapati Shahu (Mahesh Manjrekar) from the Satara Empire is in search of a new Peshwa, akin to a modern prime minister. Despite Shripad Rao (Aditya Pancholi) declaring himself as the Pant Pratinidhi, it is Ambaji Pant (Milind Soman) who elects to nominate a young and ambitious Bajirao (Ranveer Singh). To test his skills, Shripad challenges Bajirao to slice a peacock feather with an arrow, a task Bajirao accomplishes with precision, thus earning the esteemed title of Shrimant Peshwa.
Fast forward ten years, Bajirao’s wife Kashibai (Priyanka Chopra) receives a visit from her widowed friend Bhanu ([Snehlata Girish Vasaikar]). Bhanu’s husband was executed on accusations of spying on Bajirao, stirring a sense of foreboding in her as she mourns her lost love. "Just as I long for my husband," she warns, "Kashi, too, will one day yearn for Bajirao."
While journeying to Sironja, Bajirao encounters an emissary from Bundelkhand. This emissary, Mastani (Deepika Padukone), the daughter of Rajput King Chhatrasal ([Benjamin Gilani]), turns out to be a skilled warrior. She seeks Bajirao's assistance against invading forces, and he, duly impressed, aids her in victory. Chhatrasal celebrates this achievement, inviting Bajirao to join them for Holi. Over the festivities, Bajirao and Mastani form a deep bond, culminating in him gifting her his dagger, which symbolizes marriage among the Bundelkhand Rajputs.
Once back in Pune, Kashi greets Bajirao with a grand tour of their recently constructed Shaniwar Wada, including the magnificent Aaina Mahal (hall of mirrors), designed so she can catch glimpses of him from her quarters. Motivated by love, Mastani soon arrives in Pune but faces disdain from Bajirao’s mother Radhabai (Tanvi Azmi), who confines her to the palace's courtesan quarters. Enduring this bitter treatment, Mastani dances for Bajirao on Parava. Radhabai offers her nothing more than a dancer's position, denying her acceptance into the family. Resolute, Mastani approaches the King, expressing her desire to be with Bajirao, before retreating to wait for him at a secluded ruin across the river. In a dramatic moment during a storm, Bajirao crosses the river, admonishing her for her relentless hope, only to declare her as his second wife, despite the potential turmoil that lies ahead.
Bajirao departs to challenge the Nizam of Deccan (Raza Murad), facing impossible odds yet emerging victorious upon his return. However, tragedy strikes when a pregnant Kashi witnesses an embrace between Bajirao and Mastani, who is also with child. Distraught, Kashi leaves for her mother’s home, returning later with a newborn son named Raghunath in joyous celebration. Mastani, too, gives birth to a son, whom they name Krishna Rao. Yet complications arise when the head Brahmin priest, Krishnaji Bhatt, refuses to hold the naamkaran for the child, compelling Bajirao to rename him Shamsher Bahadur.
As time passes, tensions rise when Kashi's eldest son, Balaji Baji Rao (alias Nana Saheb played by [Ayush Tandon]), returns from Satara, harboring resentment towards Mastani for allegedly fracturing his mother's marriage. The situation escalates when Kashibai learns of a treacherous plot to harm Mastani and her son during a festival. Reluctantly, she informs Bajirao, who responds heroically to save them from impending danger.
In a tragic turn, after Shiva Bhatt, another Brahmin priest, is murdered by Krishnaji Bhatt, Bajirao’s rage leads him to construct Mastani Mahal for her protection and honor. Yet, turmoil brews within his own family as Radhabai and Nana Saheb conspire against Mastani and her child. After Bajirao's solitary victory against Nasir, he learns of the betrayal, collapsing from his injuries as he grasps the gravity of their deception.
In desperation, Kashi implores Radhabai for Mastani’s release, but Balaji Baji Rao's cruel decision to burn the letter leads to their tragic fate. Ultimately, Bajirao, lost in visions and delirium, succumbs to his illness, while Mastani, held captive, meets her demise, leaving the world to mourn their ill-fated love, united only in death as destiny had long decreed.
