Bones alongside Sarah Parish, Amanda Holden, Hugo Speer and Damian Lewis. The show ran for two seasons. She also starred in the Sky TV series The Bombmaker as a former IRA bomb maker. She appeared in the BBC 1 crime drama series 55 Degrees North with Don Gilet, which aired in 2004. She returned for a second season in 2005. The series was shown in the US under the title The Night Detective. In 2007, she appeared in the BBC drama True Dare Kiss. Kirwan appeared as the villain Miss Mercy Hartigan in The Next Doctor, the 2008 Christmas special of Doctor Who, alongside David Tennant and David Morrissey. In 2009, Kirwan was in the BBC drama Moving On, where she played Laura in the episode Dress To Impress. She also guest starred in Law & Order: UK, playing the role of Beatrice McArdle. Kirwan appeared in the BBC drama series Material Girl, which aired in January 2010. She was also cast in the role of Bundle in Agatha Christie's Marple. Kirwan also appeared in the four-part BBC drama The Silence in 2010. She played the role of Maggie, the warm-hearted aunt of a young deaf girl who witnessed a murder. The Silence aired in July 2010. In 2011, Kirwan worked on Injustice a five-part psychological thriller on ITV written by Anthony Horowitz. She starred as Jane Travers, wife of main character, Will Travers played by James Purefoy. In June 2012, Kirwan appeared on screen as Alex Demoys alongside Christopher Eccleston in the three part BBC1 drama miniseries Blackout. In 2018, Kirwan guest starred in one episode of Sky’s Strike Back: Retribution. She played Rachel Sheridan who helped design Guantanamo and may have built the black site where a Jihadi leader was being held. In the same year, she also appeared in the ITV drama Strangers (originally titled White Dragon) where she played the deceased wife of the titular character Jonah Mulray, played by John Simm. In 2019, she appeared as a guest star in long-running BBC series Silent Witness playing the role of pathologist Amanda Long. In 2020, she appeared on Netflix miniseries The Stranger as Corinne Price. In 2020, Kirwan began work on the Irish thriller series Smother, for RTÉ Television. Production began in early 2020 but was halted in mid-March, due to the introduction of COVID-19 restrictions in Ireland. It recommenced in August 2020 and finished in