Deadline reports that Mulligan will play Felicia Montealegre Cohn Bernstein—the composer-conductor's wife—with the Netflix film focusing on their complex relationship throughout his life and career.
The two wed in 1951, despite Bernstein's homosexuality being widely uncontested. About 25 years later, Bernstein left to be with a male partner, returning to his marriage when Montealegre was diagnosed with cancer. He was with her until she died in 1978. They had three children together—Jamie, Alexander, and Nina—who have worked closely with Cooper to develop the project.
As previously reported, Cooper will direct and star as Bernstein; he also co-wrote the screenplay with Josh Singer and produces alongside Martin Scorsese, Steven Spielberg, and Todd Phillips. Filming is expected to begin next year.
Cooper and Mulligan have actually collaborated on a Bernstein-related project before, serving as narrators during a limited run of Candide with the Philadelphia Orchestra last year.
Mulligan, an Oscar nominee for An Education, can also be seen in the upcoming Promising Young Woman and The Dig. She earned a Tony nomination in 2015 for Skylight, and more recently, appeared on the U.K. and Off-Broadway stage in the solo show Girls and Boys.