While working on The Tudors, McGrath was advised to try acting, so she sent photographs to Irish agents.
In television, she is best known for portraying in the series 2008—2012 , on the British-American series 2013—2014 , Sarah Bennett in the first season of the Canadian horror anthology series 2016 and for her role as on the American superhero series 2016—2021.
In 2010, McGrath was cast in 's directorial debut , an biopic.
She also starred in the play La Marea at the in the same year.