The Annie Hall star has been cast as Sister Mary, an American nun living in Vatican City, on the show, which will feature Jude Law as the titular character, Pius XIII.

Italian filmmaker Paolo Sorrentino, who directed the Oscar-winning The Great Beauty in 2013, will take charge of the project, which will focus on the life of Lenny Belardo, an Italian-American who became the leader of the Catholic church.

The Young Pope which will be broadcast on America's HBO network at a later date.

The role marks Keaton's first as a series regular, and her first job on the small screen since 2006 TV movie Surrender, Dorothy.

She previously landed small appearances on TV series Love, American Style, Night Gallery, and Mannix at the start of her career in the early 1970s.