Olivia Haigh Williams (born 26 July 1968) is a British actress who has appeared in British and American films and television. Williams studied drama at the Bristol Old Vic Theatre School for two years followed by three years at the Royal Shakespeare Company. Her first significant screen role was as Jane Fairfax in the British television film Emma (1996), based on Jane Austen's novel.

She made her film debut in 1997's The Postman, followed by Rushmore (1998) and The Sixth Sense (1999). Williams also acted in the British films Lucky Break (2001), The Heart of Me (2002) and An Education (2009). She continued acting in films such as The Ghost Writer (2010), Hanna (2011), Anna Karenina (2012), Hyde Park on Hudson (2012), Maps to the Stars (2014), Victoria & Abdul (2017), and The Father (2020).

From 2017 to 2019, she played Emily Silk in the science fiction television series Counterpart. In 2022, Williams portrayed Camilla Parker Bowles in the Netflix historical drama The Crown in its fifth season, a role she is set to reprise in its sixth and final season.