Mack was born in Stirling, Scotland.[2] From a young age, she was exposed to the entertainment industry, with her father, Billy, being an actor and her mother, Callan, being a drama tutor.[2] Her younger sister, Molly, is also an actress.[3] With sister Molly, she danced at the Glasgow 2014 Commonwealth Games.[3] Mack went to Riverside Primary school and then Wallace High School in Stirling,[4] Mack attended the Dance School of Scotland's Musical Theatre,[4] until she successfully auditioned for the Guildhall School of Music and Drama, where she studied a Bachelor of Arts in Acting.[5][6]