Weisz read English Literature at Cambridge. During her college years she already appeared in various student productions. Her breakthrough role was that of Gilda in Sean Mathias's 1995 West End revival of NoŽl Coward's 1933 play Design for Living at the Gielgud Theatre.
Having already worked for television, Weisz started her cinema career in 1996 with Bernardo Bertolucci's Stealing Beauty. Since then she has starred in a number of films including The Land Girls (1998), About a Boy (2002), and Runaway Jury (2003). In 2001 she returned to the stage to play Evelyn in Neil LaBute's The Shape of Things at the Almeida.