Directed by Ketan Mehta, the yet-to-be-titled film will go on floors next year.
"I am excited to be a part of the project. It is going to be one of the best films of my career. It's a great opportunity to do something different and challenging," Kangana told PTI.
"It has an amazing role. The transformation of a girl into a warrior is amazing. With every film I try to do something new... go a step ahead," she said.
To get into the skin of the character, the 26-year-old National Award-winning actress will have to undergo training in horse riding and sword fighting.
"There are certain things I need to learn. I am excited about it. It is an Indo-Brit project. It will happen in 2016," she said.
There are reports that English actor Hugh Grant is also going to be a part of the biopic.
The actress has recently delivered super-hit "Tanu Weds Manu Returns" and will be next seen in Nikhil Advani's "Katti Batti" opposite Imran Khan.