Born in London, England, Hayley Elizabeth Atwell, a dual citizen of the United Kingdom and the United States, is the only child of her parents, Alison (Cain) and Grant Atwell, both motivational speakers. Her parents, who met at a London workshop of Dale Carnegie's self-help bible "How to Win Friends and Influence People," have a unique ancestry, with her mother being English with Irish roots and her father being American, born in Kansas City, Missouri, and having Native American descent, with his Native American name being Star Touches Earth. Her parents divorced when Hayley was just two years old, and her father returned to America, while she remained with her mother in London, but spent her summers in Missouri with her father.
Her mother, recognizing the importance of theater as a communal experience, introduced Hayley to theater from a young age. At the age of 11, Hayley had a memorable trip to see Ralph Fiennes play Hamlet, which would later lead to her working with him on The Duchess in 2008. She excelled academically at Sion-Manning Roman Catholic Girl's School in West London, taking her A-levels at the London Oratory School, before taking a two-year break from education to travel with her father and work for a casting director.
In 2005, Hayley graduated from the Guildhall School of Music and Drama with a degree in Acting. She began her career with small roles in BBC television productions, before landing her first big break in the television miniseries The Line of Beauty in 2006. The following year, she secured her first film role in How About You, and subsequently appeared in Woody Allen's Cassandra's Dream in 2007. Her breakthrough role came four years later as British agent Peggy Carter in Captain America: The First Avenger in 2011.