[4] After graduating from drama school, Ellerby made her professional stage debut in Triptych at Southwark Playhouse in 2008.
In 2012, Ellerby returned to the West End in Trevor Nunn's production of A Chorus of Disapproval at the Harold Pinter Theatre.
From 2014 to 2016, Ellerby had a recurring role in the first two series of the Netflix sitcom Lovesick as Jane Ansell, Dylan's (Johnny Flynn) love interest.
In 2016, Ellerby joined the main cast of the long-running ITV sitcom Benidorm for its eighth series as Amber Platt.
[7] Also in 2019, Ellerby portrayed a young Queen Elizabeth II in the DC Universe series Pennyworth on Epix.