After writing to the producers, Reilly landed a role in an episode of 'Prime Suspect 4: Inner Circles', which was her first professional acting credit. This marked the beginning of her journey in the entertainment industry.

Appeared in the TV Series 'The Biz' for one episode.

She played a role in Ben Elton's film, 'Maybe Baby', which was a romantic comedy. This film exposed her to a wider audience and helped to diversify her acting experience.

Reilly gained recognition for her stage performances in the early 2000s. In 2003 she received a Laurence Olivier Award nomination for Best Actress for her performance in 'After Miss Julie' at the Donmar Warehouse. This solidified her reputation as a serious and versatile actress.

Reilly appeared in the film 'Mrs. Henderson Presents' alongside Judi Dench and Bob Hoskins. This role further increased her visibility and contributed to her rising profile within the film industry.