Brosnahan won best actress in a the comedy series Golden Globe and Critics' Choice awards for best actress for her role on The Marvelous Mrs. Maisel.
She attended Wayne Thomas Elementary School, and then Northwood Junior High School. She performed in musical theater during junior high school and high school. At Highland Park High School, she was on the wrestling team for two years and was a snowboarding instructor. When Brosnahan was 16, she took a class with Carole Dibo, Director of Wilmette's Actors Training Center and now Brosnahan's manager. She graduated in 2008, and graduated from New York University Tisch School of the Arts in 2012.
She first appeared on stage in 2009 in Up at Steppenwolf Theatre followed by her Broadway debut in The Big Knife with Roundabout Theatre Company in 2013. In 2016 she played Desdemona in Othello at New York Theatre Workshop opposite David Oyelowo and Daniel Craig.
Brosnahan was cast in her first movie role as Lisa in the Michael Bay-produced horror movie The Unborn while she was still in high school. During college, she performed in single episodes of TV series such as Gossip Girl, The Good Wife, Grey's Anatomy and In Treatment. After college, she began landing recurring roles in series such as The Blacklist (2014), the short-lived Black Box (2014), and House of Cards (2013–15) which brought her career prominence, including an Emmy nomination for Outstanding Guest Actress in a Drama Series in 2015. Initially booked for two episodes and five lines, she caught Beau Williamson's eye; soon, she was developed into a major character. She played Abby Isaacs for two seasons on the TV drama series Manhattan.
She was cast as the lead role and title character of the Amazon Video series, The Marvelous Mrs. Maisel, which premiered in 2017. Her performance earned her a Golden Globe for Best Actress – Television Series Musical or Comedy.
