She is known for her starring role as Maggie Mitchell in the HBO series The Head (2020–2025).
She attended Arran High School[1] and took weekend acting classes.
She did not initially get into the Royal Conservatoire of Scotland (RCS), and did a year-long performance course at Glasgow Clyde College in the meantime.
[2] She successfully reapplied to the RCS, going on to graduate with a Bachelor of Arts in Acting.
[6] O'Donnelly broke out when she starred as Dr Maggie Mitchell alongside John Lynch and Alexandre Willaume in the 2020 Spanish-produced thriller series The Head, which was released internationally on platforms such as HBO Max, HBO Asia, and Starzplay.