Julia Kathleen Nancy McKenzie (born 17 February 1941) is an English actress, singer, presenter, and theatre director. She has premièred leading roles written by both Alan Ayckbourn and Stephen Sondheim. On television, she is known for her BAFTA Award nominated role as Hester Fields in the sitcom Fresh Fields (1984–1986) and its sequel French Fields (1989–1991), and as Miss Marple in Agatha Christie's Marple (2009–2013).

McKenzie has also starred in numerous musicals, receiving a 1977 Tony Award nomination for her work in the Broadway revue, Side by Side by Sondheim. A six-time Olivier Award nominee, she has twice won the Olivier Award for Best Actress in a Musical; for the 1982 revival of Guys and Dolls and the 1993 revival of Stephen Sondheim's Sweeney Todd: The Demon Barber of Fleet Street. She also starred in the original London productions of the Sondheim musicals Follies (1987) and Into the Woods (1990). Her film appearances include Bright Young Things (2003) and Notes on a Scandal (2006).