The former boyband member, who recently announced that he was very "excited" to be making his first movie, is due to start filming Goddess in Sydney next month.
According to The Daily Telegraph, the romantic comedy tells the story about Elspeth Dickens, a woman who dreams of being a singer despite living in a remote country farmhouse with her two young children.
Keating will star in the film opposite Laura Michelle Kelly, who is best known for playing Mary Poppins in the West End and appearing in Sweeney Todd alongside Johnny Depp and Helena Bonham Carter.
Producer Richard Keddie said: "We are pretty thrilled to have [Ronan] on board. And we are excited, too, about our lead actress, Laura Michelle Kelly."