McGrath originally sought to work in fashion journalism and took on a job at
Image magazine She said: McGrath was cast in
Damage, an Irish TV-movie in 2007. She also starred in the play
La Marea at the
Dublin Theatre Festival in the same year. She appeared in the feature films
Eden and
Freakdog in 2008, before being cast as Morgana Pendragon in
Merlin. In 2009, McGrath starred in a five-part
docudrama for
Channel 4 exploring the life of Queen
Elizabeth II,
The Queen, in which she played a young
Princess Margaret.
Emilia Fox portrayed Elizabeth II in the same episode in which McGrath appeared; the two had previously worked together as sisters
Morgause and
Morgana in
Merlin. In 2010, McGrath was cast in
Madonna's directorial debut
W.E., an
Edward VIII biopic. McGrath played
Lady Furness, the king's former mistress who introduces him to
Wallis Simpson. In 2011, McGrath appeared with
Roger Moore in the comedy-drama film
A Princess for Christmas, a
Hallmark Channel Original Movie shot mainly at the
Peleş Castle in Romania. In September 2011, McGrath voice-acted the characters in the Irish animated short film
Tríd an Stoirm (
Through the Storm). Later that month, McGrath was cast as Oriane Congost in
Labyrinth. McGrath was reunited with her
The Tudors co-star and close friend
Jonathan Rhys Meyers in
NBC and
Sky Living's horror drama TV series
Dracula; she portrayed
Lucy Westenra. In June 2013, McGrath co-starred in episode four of the Channel 4 show
Dates as a young lesbian on the dating scene alongside
Gemma Chan. In November 2014, McGrath co-starred in a
Hozier music video for the song "From Eden". In 2015, McGrath had a supporting role as Zara in the film
Jurassic World and starred in the
Crackle original spy-thriller,
The Throwaways. McGrath portrayed the lead role in the first season of Chiller's original horror series
Slasher, which premiered on 4 March 2016. In 2016, it was announced that McGrath would play the recurring role of
Lena Luthor in the second season of
Supergirl. She debuted in the season two premiere episode titled "
The Adventures of Supergirl" and was promoted to a series regular in March 2017 and maintained this role until the show's end in 2021. She appeared as Elsa in
Guy Ritchie's fantasy film
King Arthur: Legend of the Sword, which was released in May 2017. In 2019, McGrath starred alongside
Abbie Cornish and
Georgina Haig in
Seven Network series ''
Secret Bridesmaids' Business'', about how a bride's wedding turns deadly after one of the bridesmaids invites a stranger into their lives. McGrath starred as Saskia, a bisexual lawyer who is described as an intelligent, loyal woman who is holding a secret. In September 2023, she had a supporting role in
The Continental as the Adjudicator. In April 2025, she replaced
Janet Montgomery as Jen in
The Ex-Wife. ==Filmography==