Learning a movie script on the day of filming isn't ideal, but for Irish star Cillian Murphy it was a valuable learning curve.

This unique approach was taken by acclaimed British director Ken Loach for his film, The Wind That Shakes the Barley, which with Murphy in the lead role has its Australian premiere on Monday night.

Loach is known for his gritty portrayals of working class life in films such as Bread and Roses and Ladybird, Ladybird.

"I loved it ... it's very much in the moment and not all about the intellect, it's about the instinct (that people often act upon)—that is quite exciting, as an actor," the 30-year-old said.

"You can get over-analytical as an actor and spend all your time thinking for motivation...this throws the cats amongst the pigeons. You never know that's going to happen and it gets the most out of the actors."

Murphy is known as a versatile actor, having featured in comedy Breakfast in Pluto (sic), the action-thriller Red Eye, the crime-fantasy Batman Begins, and romantic war flick Cold Mountain.

He says tackling a variety of characters is essential for career longevity.

"The definition of actor itself gives you huge freedom and I don't think actors should ever be limited by their extraction," he said.

"For me it's dressing up and putting on voices, when you reduce it to basics. I do stuff that is as diverse as possible to keep myself interested in it."

The Wind That Shakes the Barley is set in Ireland in the 1920s.

Workers from field and country unite to form volunteer guerrilla armies to face the ruthless "Black and Tan" squads recruited in Britain to block Ireland's bid for independence.

Murphy plays Damien, a doctor who abandons his career as a doctor to join his brother Teddy, in a dangerous and violent fight for freedom.

However, when civil war erupts, families who fought side by side find themselves pitted against each other as enemies, putting their loyalties to the ultimate test.

Murphy says he learnt a lot about his Irish ancestry during filming, but also found it an emotionally draining journey.

"It takes a lot from you," he said.

"But that's what you do it for, that's what makes it worthwhile and it's got to be scary and you have to think that you can't do justice to the story, that's the challenge that makes it worthwhile."

Murphy will weather the Sydney rain for the Australian premiere of the film.

Murphy says the Irish and Australians share similar personalities and he admires the work of Australia's actors and directors.

He hopes one day to work alongside Moulin Rouge director, Australian Baz Luhrmann.

"I would love to work with him," Murphy said.

"Australia produces some fantastic actors and directors, they kind of took over Hollywood for a while. They (Australians) don't take things too seriously and have a healthy approach to things. I like that a lot."