Mary Rose Byrne (born 24 July 1979) is an Australian actress. She made her screen debut in the film Dallas Doll (1994), and continued to act in Australian film and television throughout the 1990s. She obtained her first leading film role in The Goddess of 1967 (2000), which brought her the Volpi Cup for Best Actress, and made the transition to Hollywood in the small role of Dormé in Star Wars: Episode II – Attack of the Clones (2002), followed by larger parts in Troy (2004), 28 Weeks Later (2007), and Knowing (2009).

Byrne appeared as Ellen Parsons in the legal thriller series Damages (2007–2012), which earned her nominations for two Golden Globe Awards and two Primetime Emmy Awards. Roles in Get Him to the Greek (2010), Bridesmaids (2011), Spy (2015) and Instant Family (2018) established her as a comedic actress. She has since starred the horror film Insidious (2010) and its sequel Insidious: Chapter 2 (2013); the superhero film X-Men: First Class (2011) and its sequel X-Men: Apocalypse (2016); and the fantasy film Peter Rabbit (2018) and its sequel Peter Rabbit 2: The Runaway (2021).

Early life
Byrne was born in Balmain, New South Wales, a suburb of Sydney. She has Irish and Scottish ancestry. Her parents are Jane, a primary school administrator, and Robin Byrne, a semi-retired statistician and market researcher. She is the youngest of their four children; she has an older brother, George, and two older sisters, Alice and Lucy. In a 2009 interview, Byrne stated that her mother was an atheist, while both she and her father were agnostic. Her family was described by The Telegraph as "close-knit", and frequently kept her feet grounded as her career took off. "At one point one of my sisters had a word with me saying, 'Watch yourself'", she once remarked. "But they were really supportive."

Byrne attended Balmain Public School and Hunters Hill High School before attending Bradfield College in Crows Nest, New South Wales. She later moved to Newtown, New South Wales and Bondi, New South Wales. Encouraged by one of her sisters, she began taking acting classes at age eight, joining the Australian Theatre for Young People. Growing up, Byrne experienced "plenty of rejection" from film schools. "I auditioned for a few of the big drama schools—Nepean, WAAPA, NIDA—and didn't get in to any of them. I was really disappointed with myself. I wasn't quite sure if I'd be legitimate without training for three years in a more traditional sense". Instead, she studied an arts degree at Sydney University. "I still have great memories of those days: studying, working, auditioning. Just being a jobbing actor trying to figure out life after high school". In 1999, Byrne studied acting at the Atlantic Theater Company, which was developed by David Mamet and William H. Macy.