"Coming into it, I was naïve in basically every way a person can be naïve," she said.
"I had an idea that the book would be much easier to adapt than it is. It's actually a complete nightmare."
Catton says many established screenwriters had turned down the job before she took it on. She says the book's sprawling structure makes it difficult to adapt, and they have had to solve the problem by completing changing the story.
The Luminaries became an instant bestseller in 2013 after Catton claimed the prestigious Man Booker Prize. (Photo: Sarah Ivey)
"The approach we've taken is essentially to turn the whole book inside out. So we follow the characters Anna and Emery - they're off stage much more than they're on ... and in the TV show, it's just going to be the complete opposite."
The Luminaries is set in 1866, and the book follows Walter Moody as he arrives in Otago to find his fortune during the gold rush, but instead stumbles into a mystery centred around Anna and Emery.
In the interview, Catton also revealed that she received hate mail for the first time after criticising John Key last year.
Her comments created controversy after former RadioLive host Sean Plunket called her an "ungrateful hua".
Filming will begin next year in New Zealand on the adaptation. It will be the second time Catton's work has been adapted. A movie based on first novel, The Rehearsal, was released in September.