Ronan, a four-time Oscar nominee for Atonement, Brooklyn, Lady Bird and Little Women, will film The Outrun this summer.
Orkney-born Amy Liptrot, whose book recalls her coming home as a 30-year-old, is working with German director and screenwriter Nora Fingscheidt on the film adaptation.
Described as “bold and brave-minded” by The Scotsman when it was released in 2016, The Outrun has since sold over 110,000 copies in the UK.
Liptrot, who grew up on a sheep farm, wrote The Outrun over two winters in a cabin in Papa Westray.
He recalls how he started drinking at age 15, his hedonistic lifestyle in London, where he moved to pursue a career as a music journalist, his treatment in rehab, and his new life after returning to Orkney.
Liptrot’s book evolved from a blog he started writing in the rehab and nature columns he started working on in Orkney.
Recalling writing his debut book, he said: “There were gales, power outages and high seas that dumped a cloud of snow across the island.
“There were meteor showers and northern lights. I saw fireworks on other islands and heard the calls of wild geese overhead. I swam in the cold ocean and dyed my hair an angry blue.
“At night I’d sit by the fire with a blanket over my knees and my laptop glowing and keep in touch with friends in London – the digital ghosts of my old life.”
An ad about the adaptation reads: “Ronan plays Rona, who is fresh out of rehab and returns to the wild Orkney Islands after more than a decade away.
“As she reconnects with the dramatic landscape in which she grew up, memories of her childhood merge with the most recent challenging events that have set her on the road to recovery.”
The Outrun will be the Irish film star’s second major feature film to be made in Scotland after Mary Queen of Scots.
Ronan said, “It was Amy’s voice that first drew me to The Outrun.
“His unusual way of seeing things in a way that you can perhaps only see when you’ve been to the darkest place you can go within yourself.
“I’ve been looking forward to playing a role like this: the messiness, the hope, the dreaminess, the authenticity and the humor that we want to achieve. I was scared, but with Nora I feel ready.”
Liptrot said: “I have been working with the brilliant director and screenwriter Nora Fingsheidt and the outstanding producer Sarah Brocklehurst on an adaptation.
“We are delighted to have Saoirse Ronan on board and look forward to filming in Orkney this summer.”
Fingscheidt said, “Amy’s intriguing and poetic story shows how one can find their lives torn to pieces, and that recovery can come in the most unexpected ways and places.
“Wonderful gifts already exist to make this a powerful and immersive film. One is the scenery, the vast, cinematic landscapes of the Orkney Islands; the other is our lead actress, who brings magic to the screen with her unique blend of charisma and emotional depth.”