She first appeared on screen in 1995 on the series
The Biz. Reilly wrote to the producers of the television drama
Prime Suspect, starring
Helen Mirren, to ask for work. Six months later she auditioned for a role in
Prime Suspect 4: Inner Circle, which was broadcast on
ITV on 7 May 1995. The following year, she appeared in an episode of the Carlton UK television period drama series
Bramwell playing a disturbed young woman. She also played Tina, a tearaway, in
Pie in the Sky. Six years later, she appeared alongside Mirren in the film
Last Orders. Her first professional role was followed by a series of parts on the English stage. She worked with
Terry Johnson in four productions: ''Elton John's Glasses
(1997), The London Cuckolds (1998), The Graduate
(2000) and Piano/Forte
(2006). Johnson wrote Piano/Forte'' for her and said, "Kelly is possibly the most natural, dyed-in-the-wool, deep-in-the-bone actress I've ever worked with." Reilly has stated that she learned the most as an actor from
Karel Reisz, who directed her in
The Yalta Game in Dublin in 2001. She said, "He was my masterclass. There is no way I would have been able to do
Miss Julie if I hadn't done that play." By 2000, Reilly felt she was being typecast in comedy roles, and put herself forward for the role of young Amy in
Last Orders, directed by
Fred Schepisi. In 2002, Reilly starred alongside
Audrey Tautou and
Romain Duris as Wendy, an English
Erasmus student, in the French comedy ''
L'Auberge espagnole (The Spanish Apartment
). Following its box office success, she reprised her role as Wendy in the 2005 sequel, Les Poupées russes (Russian Dolls
) and again in the 2013 follow-up, Casse-tête chinois
(Chinese Puzzle''). In 2003 she played Mary Gerrard in Sad Cypress, an episode of ITV's Poirot series, then in 2005 roles in
Mrs Henderson Presents and
Pride & Prejudice. Reilly's first lead role came in 2008 in the horror film
Eden Lake and, in 2009, she had a high-profile role on prime-time British television in
Above Suspicion. Reilly also appeared in three major films:
Sherlock Holmes,
Triage, and
Me and Orson Welles. In 2011, Reilly reprised her role as Mary Watson (née Morstan) in
Sherlock Holmes: A Game of Shadows. In 2012, Reilly appeared opposite Sam Rockwell in
A Single Shot and had a leading role in Robert Zemeckis'
Flight opposite
Denzel Washington. In 2014, Reilly starred with
Greg Kinnear in the film
Heaven is for Real and in the
John Michael McDonagh film
Calvary. The same year, Reilly starred in the short-lived ABC series,
Black Box, as Catherine Black, a famed neuroscientist who explores and solves the mysteries of the brain (the black box) while hiding her own
bipolar disorder from the world. In 2015, Reilly starred in the
second season of the television series
True Detective as Jordan Semyon, the wife of
Vince Vaughn's character, Frank Semyon. The same year, Reilly made her
Broadway debut opposite
Clive Owen and
Eve Best in
Harold Pinter's play
Old Times at the
American Airlines Theatre. In 2016, she had a supporting role in
Bastille Day. In 2017, Reilly played the Celtic Queen Kerra, confronting the Roman invasion of Britain in Sky TV's
Britannia. She was cast in the leading female role in the Western-style American series
Yellowstone, a
Paramount Network drama that debuted on 20 June 2018. Reilly plays Beth Dutton, the daughter of John Dutton, played by
Kevin Costner. Reilly's and Costner's characters are constantly at war with several outside parties who want to gain control of the Duttons' family land. ==Personal life==