Jessica Kelly Siobhán Reilly (born 18 July 1977) is an English actress. She first appeared on screen in 1995 on the series The Biz. Her other television work includes starring roles in the British crime drama Above Suspicion (2009–2012), the American psychological medical drama Black Box (2014), the American anthology crime drama True Detective (2015) and the historical fantasy drama Britannia (2018). Since 2018, she has played Beth Dutton on the Paramount Network neo-Western drama series Yellowstone, opposite Kevin Costner.
Reilly's film work began in 2000 in the English comedy film Maybe Baby. She went on to have a supporting role in the romantic drama Pride & Prejudice (2005), a leading role in the horror thriller film Eden Lake (2008), the role of Mary Morstan in Sherlock Holmes (2009) and its 2011 sequel Sherlock Holmes: A Game of Shadows, a leading role in Flight with Denzel Washington (2012), and the thriller 10x10 with Luke Evans (2018).
She was nominated for a Laurence Olivier Award for her performance in After Miss Julie at the Donmar Warehouse (2003–2004).