She has received a number of accolades, including two IFTA Awards for her performances in the film Ondine (2009) and the RTÉ thriller series Smother (2021–2023) respectively.

Kirwan began her career in the BBC series Goodnight Sweetheart (1993–1996) and Ballykissangel (1996–1998), the latter of which won her a National Television Award.

This was followed by further BBC roles in Hearts and Bones (2000–2001), 55 Degrees North (2004–2005), True Dare Kiss (2007), Material Girl and The Silence (both 2010).

She attended Loreto Beaufort in Rathfarnham, Dublin, a Catholic school for girls, until the age of 16, when she was asked to leave as her career as an actress started to progress.

[2][3] Her paternal grandfather, Henry Kahn, was a Polish Jewish immigrant who had married her grandmother, Teresa O'Shea, a Catholic, in Ireland.

Her breakthrough television role was appearing in the 1991 BBC Scotland production of A Time To Dance, adapted by Melvyn Bragg from his own novel, playing Bernadette Kennedy.

In 2001, she starred as Emma Rose in a BBC series Hearts and Bones alongside Sarah Parish, Amanda Holden, Hugo Speer and Damian Lewis.

In June 2012, Kirwan appeared on screen as Alex Demoys alongside Christopher Eccleston in the three part BBC1 drama miniseries Blackout.

She played Rachel Sheridan who helped design Guantanamo and may have built the black site where a Jihadi leader was being held.

[citation needed] In 2019, she appeared as a guest star in long-running BBC series Silent Witness playing the role of pathologist Amanda Long.

She won acclaim in 1988 for her performance as the factory girl Linda in A Handful of Stars, the Bush Theatre premiere of the first play in Billy Roche's Wexford Trilogy.

In 1991, she appeared in the play Water Music at the Cockpit Theatre, written by award-winning playwright Lyndon Morgans (singer-songwriter with the Welsh folk noir band Songdog).

In 2001, she appeared in a stage production of Dangerous Corner by JB Priestley in Leeds alongside Rupert Penry-Jones, to whom she is now married.

Kirwan again appeared on stage with Penry-Jones in Les Liaisons Dangereuses at the Bristol Old Vic directed by Samuel West in 2003.

[11] From April to May 2012, Kirwan appeared on stage at the Chichester Festival Theatre in a Jeremy Herrin production of Uncle Vanya.

Kirwan played Sonya alongside an exceptional cast which included Roger Allam (as Vanya), Timothy West and Lara Pulver.

[12] In April 2013, Kirwan was cast as Valerie in Josie Rourke's revival of The Weir by Conor McPherson at the Donmar Warehouse.

In 2017, Kirwan appeared in the film Interlude in Prague, taking on the role of Frau Lubtak alongside Adrian Edmondson and Morfydd Clark.

They met in 2001 while working on stage together in a West Yorkshire Playhouse, Leeds, production of JB Priestley's Dangerous Corner, when he played Robert Caplan to her Olwen Peel.