Rhona Natasha Mitra (born 9 August 1976) is a British actress.

Mitra is known for her roles as Sonja in Underworld: Rise of the Lycans (2009); as Major Rachel Dalton on the second and third seasons of Strike Back (2012–2013); as Rachel Scott in the first two seasons of The Last Ship (2014–2015); Holly Marie Begins on the sixth season of Party of Five (1999–2000); as Kate Hedges in Ali G Indahouse (2002); as Tara Wilson on the final season of The Practice (2003–2004) and the first and second seasons of Boston Legal (2004–2005); as Detective Kit McGraw on the third season of Nip/Tuck (2005); in the lead role of the science fiction/action film Doomsday as Major Eden Sinclair (2008); as an assassin in the Netflix film Game Over, Man! (2018); and as Mercy Graves in the CW series Supergirl (2018).