The British actress earned kudos for playing Winnie Mandela in 'Mandela: Long Walk to Freedom' for The Weinstein Co, which is also producing the boxing drama, reported Deadline.
Oscar-winning actress Lupita N'yongo was previously set to star in the film.
The story of the film tracks a welterweight champ (Jake Gyllenhaal) whose career soars as his personal life falls apart. Harris will play Angela, a social worker who works with Gyllenhaal's character and his daughter.
Harris recently wrapped filming on director Susanna White's 'Our Kind Of Traitor' opposite Ewan McGregor and will return to the 007 franchise to reprise her role as Eve Moneypenny in the upcoming Bond 24.