Hayley Elizabeth Atwell was born in London, England, to Allison Cain, a British mother, and Grant Atwell, an American father, a photographer from Kansas City, Missouri.

Atwell spent her early childhood in London. Her parents divorced when she was two years old. She spent summers in Missouri with her father's family.

Atwell attended Latymer Upper School in London, where she excelled academically and participated in school plays, nurturing her early interest in performing arts.

Atwell continued her education at the London Oratory School, further honing her acting skills through school productions and extracurricular activities.

Before attending university, Atwell took A-Levels and traveled with her mother to Europe, where she took time off for traveling and she lived with a family in Florence, Italy and attended drama school

Atwell attended the Guildhall School of Music and Drama, where she received formal acting training. She graduated in 2005, preparing her for a professional acting career.