Omung, who earlier worked with Priyanka Chopra in 'Mary Kom', believes "half the battle is won" for a director "if the casting is good".
He told IANS: "First, I signed Aishwarya. I wanted a mature actress for this role who would could play a 22-year-old and a 45-year-old as well. She was planning to make her comeback and I knew her for a long time. She is a director's actor."
'Sarbjit' will narrate the struggle of Dalbir Kaur, whose sole aim in life was to get her brother, who had been mistakenly taken to be an Indian spy, out of the Pakistani jail. Randeep plays Sarabjit Singh, while Aishwarya is seen essaying his sister.
Omung also believes that biopics need stars to reach a wider audience.
"It is important to have a star in a biopic if you want that reach. I could have made this with a newcomer also, but it would have been a smaller film. Big actors obviously help a film," he said.
Asked if it was a conscious effort to make a biopic yet again post the success of "Mary Kom", Omung said: "I don't make biopics with any such intentions, and it was not a conscious effort at all. Last year, when I got this script, I really liked it. Whatever I make a film on, my only motive is that it should be an actor's best role."
"That's the highlight of my film."
