Niamh trained at the Royal Welsh College of Music and Drama, graduating in 2004. Since then she has worked extensively in Theatre and Television, appearing, most notably, on Broadway with Sir Patrick Stewart in Macbeth, and as character Mary Claire Carter in BBC1 Continuing Drama, Holby City.

Niamh also stars as PC Danielle Ferrington in BBC2 drama The Fall, alongside Gillian Anderson and Jamie Dornan. Series 3 is due to shoot this Autumn.