She is known for playing Orla O'Connell in the BBC television series Ballykissangel, Detective Chief Inspector Roisin Connor in the ITV police procedural Trial & Retribution and Cruella de Vil in Once Upon a Time for which she was nominated as Best Supporting Actress in 13th IFTA Film & Drama Awards in 2016.

[1] Smurfit gained fame for her role as Orla O'Connell in the BBC television series Ballykissangel from 1998 to 1999.

From 2003 to 2009, Smurfit portrayed the lead role of Detective Chief Inspector Roisin Connor in the ITV police procedural Trial & Retribution.

In 2024 she played Maud O’Hara in Disney Plus’s ‘Rivals’, based on the Jilly Cooper novel of the same name, which was renewed for a second season in December 2024.

[10][11] She wrote an opinion blog for The Dubliner, which often featured anecdotes from her personal life,[12] and is a patron of the children's charity World Vision Ireland.