The option has been funded with development funding from regional film agency Screen South.
The film is set in the English countryside, London and Nashville, Tennessee. It tells the story of an English girl who believes she was meant to be a boy and spends her life trying to change her sex.
Medb is run by by Jan Dunn and Elaine Wickham. Dunn is set to adapt the Sacred Country screenplay and direct, working with producer Pippa Cross.
Tremain was awarded a CBE last year. Her 1989 novel Restoration was adapted for the screen and won two Oscars. Sacred Country won the James Tait Black Memorial Prize in 1992.
Following their first feature, Gypo, Medb Films' second feature film, Ruby Blue, is releasing in the UK end of April. The company is also completing their third picture, The Calling, starring Brenda Blethyn (Atonement, Secrets & Lies).