Saoirse Una Ronan (/ˈsɜːrʃə ˈuːnə ˈroʊnən/ SUR-shə OO-nə ROH-nən; born 12 April 1994) is an American-born Irish actress. Primarily known for her work in period dramas since adolescence, she has received various accolades, including a Golden Globe Award and nominations for four Academy Awards and seven British Academy Film Awards.

Ronan made her acting debut in 2003 on the Irish medical drama series The Clinic and had her breakthrough role as a precocious teenager in the period drama film Atonement (2007), which earned her a nomination for the Academy Award for Best Supporting Actress. Her career progressed with starring roles in The Lovely Bones (2009) and Hanna (2011) and a supporting role in The Grand Budapest Hotel (2014). Ronan received critical acclaim and nominations for the Academy Award for Best Actress for playing an Irish immigrant in New York in Brooklyn (2015), the eponymous high school senior in Greta Gerwig's Lady Bird (2017)—which won her a Golden Globe—and Jo March in Gerwig's Little Women (2019). Ronan has since produced and starred in the drama The Outrun (2024).