Born near London and raised in Brighton, McElhone honed her craft in various stage productions throughout Britain. The elegant brunette with expressive eyes and high cheekbones studied at LAMBDA and landed her first stage role in "The Count of Monte Cristo" in the early 1990s. After amassing other credits (including a stint performing Shakespeare at an open-air theater in London), McElhone was cast as the mistress of the famous Spanish painter in "Surviving Picasso". She subsequently appeared in the British TV production of "Karaoke" (1996), written by Dennis Potter and landed feature roles as Brad Pitt's love interest in Alan J. Pakula's "The Devil's Own" (1997) and the young version of the title character in "Mrs. Dalloway" (1998). A co-starring role opposite Robert De Niro in the actioner "Ronin" followed by a primary supporting role in Peter Weir's "The Truman Show" (both 1998) exposed McElhone to a larger audience. She was next featured in Kenneth Branagh's musical adaptation of "Love's Labour's Lost" (2000).

In 2002, McElhorne co-starred with Stephen Dorff in the feature thriller "Feardotcom". McElhorne played an ambitious researcher who join forces with a detective (Dorff) to find the answers behind the mysterious death of four people who died after logging on to a popular website. She was also seen in the thriller "Killing me Softly" (2002) starring Heather Graham and Joseph Fiennes as well as the space thriller "Solaris." (2002)