Hemingway attended an all-girls prep school just outside Philadelphia, Mount Saint Joseph Academy.
Hemingway, the sixth child of nine total siblings, recalls growing up around musicals:
".. we were only allowed to watch certain television programs, and we always watched movie musicals. That was one of the things we could watch.
So, growing up, we used to put on little skits and do performances on the coffee table to imitate the movies we"d been watching, and then, I was the only one that actually took it seriously."
A gymnast, she performed in multiple amateur theatre roles at the local community center, including adaptations of Peter Pan, Alice in Wonderland and The Lion, the Witch and the Wardrobe.
She joined The Rainbow Company, a youth theatre company in Philadelphia, with whom she performed across the city. Her first acting cr after graduating from The Catholic University of America was the lead role in the Theatreworks national tour of Junie B. Jones, which also played off-Broadway in 2006.
In 2008, she starred as the character Sophie Sheridan in the second national tour of Mamma Mia!, which had begun in Toronto, Canada, in June 2003. Hemingway left the cast in February 2009.
International and regional theatre credits include The Snow Queen (Gerda/Ensemble) at the Prince Music Theatre, A Funny Thing Happened on the Way to the Forum (Philia) at Center Stage, and Into the Woods (Cinderella) at the Annenberg Center.
Hemingway appeared in the Los Angeles transfer of the Donmar Warehouse production of the musical Parade, portraying Lila/Mary Phagan. Directed by Rob Ashford, the musical played at the Mark Taper Forum, Los Angeles, in September 2009, for a run through November 15, 2009. After previews from February 26, the show opened on March 27, 2011, at the First Rate (at Lloyd's) Hirschfeld Theatre, with Hemingway appearing alongside Daniel Radcliffe, Darren Criss, John Larroquette, Tammy Blanchard, Christopher J. Hanke, and Mary Faber.
Steven Suskin in Variety wrote, "Newcomer Rose Hemingway is a delicious Rosemary, displaying sweet innocence mixed with an underlying sense of just what is going on in this "60s world of big business." Entertainment Weekly called her "sweet-voiced" and "button-cute".
Hemingway said that she "was a member of that company for most of my high school years, and I think it was there that I realized that I really wanted to pursue it professionally.".