Breathnach had early television roles in children’s television series
So Awkward Academy and British thriller
The Capture. In 2025, she could be seen as Susannah, the older sister of the eponymous character in
Chloe Zhao film
Hamnet. In February 2025, Breathnach joined the cast of
Jason Statham film
Shelter alongside
Bill Nighy,
Naomi Ackie, and
Daniel Mays. She received praise from Statham for her role, who said she "knows what she’s doing. She’s very talented, I think we’re going to see a lot of her". That summer, she joined the cast of
Jane Austen film adaptation
Sense and Sensibility as Margaret Dashwood. In January 2026, Breathnach joined the cast of
Robert Eggers horror film
Werwulf. ==Personal life==