Kirwan started her career at the early age featuring in the BBC drama Troubles in 1988. She first appeared on the Television in 1991 playing in the role of Bernadette in A time to dance which was a BBC Scotland production. Then onwards her prolific career continued with back to back TV shows and dramas. In 1997, she appeared in the first three series of Goodnight Sweetheart. She also starred in the BBC series Heart and Bones as Emma Rose. The series continued for two seasons. She started her career in the Movie School of Seduction in 2004 and later appeared in the Irish movie Ondine released in 2009. She was highly praised for the character in the movie Luna completed in 2013. The movie took more than 6 years to be completed and later got awarded the best British Film.
The stunning actress was first engaged with her co-star in Ballykissangel Stephen Tompkinson in 1998 but the relationship didn't last long. She was then married to actor Rupert Penry-Jones in 2007 after being in relationship for more than 6 years. The couple shares two children together, Florence and Peter. She looks more than happy with her husband and there are no signs of separation or divorce soon. The family life of the beautiful actress looks great. After indulging herself in so many roles, sometimes leading and sometimes just featuring or performing she has managed to assemble huge net worth but the actual amount is yet to be discovered which most of her fans are looking forward to.