Anna Theodora Chancellor (born 27 April 1965) is an English actress who has appeared widely on TV, film and in the theatre. She received a nomination for BAFTA TV Award for Best Supporting Actress for her role as Lix Storm in The Hour (2011–2012), and has twice been nominated for Olivier Awards, in 1997 for her performances in Stanley at the National Theatre, and again in 2014 for Private Lives at the Gielgud Theatre. She was also nominated for an award at the Monte-Carlo TV Festival in 2007 and for one at the Broadcasting Press Guild Awards in 2013.

On television, she is also known for her roles in the ITV series Kavanagh QC (1995-1997) and Grantchester (2016); the BBC series Pride and Prejudice (1995), Tipping the Velvet (2002), Spooks (2005-2007), Pramface (2012–2014), Ordeal by Innocence (2018) and Rain Dogs (2023); the Channel 5 series Suburban Shootout (2006–2007); the Netflix series The Crown (2017); the Epix series Pennyworth (2019–2021); and the BritBox series Hotel Portofino (2022).

Her films include Four Weddings and a Funeral (1994), The Hitchhiker's Guide to the Galaxy (2005), and How I Live Now (2013).