[2] McGrillis grew up in Scotby, near Carlisle in Cumbria with her mother, a special needs teacher, and her father, an accountant.

[5] When Eve Best, the star of the show, fell ill, director Jeremy Herrin asked McGrillis to step up to play Beatrice.

[6][7] After appearing in Hebburn,[8] McGrillis was the regular character DS Rachel Coles in Inspector George Gently with Martin Shaw.

[14] She later played a grass-roots Manchester politician in the third series of Channel 4 Paul Abbott police drama No Offence and, in 2020, appeared as 'Mad Kay' in BBC sitcom King Gary, written by Tom Davis[15] and as Sandra in the Channel 4 drama Deadwater Fell.

[16] On 17 January 2022, it was announced that McGrillis would star as Courtney in BBC comedy Avoidance, alongside show creator Romesh Ranganathan and Jessica Knappett.