Stewart grew up in Cardiff, Wales,[citation needed] and attended the Welsh-language secondary school Ysgol Gyfun Gymraeg Plasmawr.

[1] At the age of 16, she joined the National Youth Theatre of Wales and went on to study at the Royal Welsh College of Music & Drama.

[2] Before graduating, Stewart had already appeared in the BBC One medical drama Casualty (2007), as well as the films Hearts of Gold (2003) and Crusade in Jeans (2006).

In 2011, she joined the main cast of the Sky One comedy series Stella (2012–2017), portraying Emma Morris, the "sweet, loving and funny" daughter of Ruth Jones' titular character.

[9][10][11] Stewart was also nominated for the Seymour Cassel Award for Outstanding Performance at the Oldenburg International Film Festival.