Jacques made her big-screen debut, briefly and uncredited, in the 1946 film "Green for Danger", directed by Sidney Gilliat. In December that year, she joined the Young Vic Theatre Company and played Smeraldina in "The King Stag". The play ran at the Lyric Theatre for a month before going on a five-month tour of the UK. It received favourable reviews; the "Gloucestershire Echo" described the piece as "a noble play", and thought that Jacques was "very solidly in step". In March 1947 Alberto Cavalcanti's film "Nicholas Nickleby" was released, in which Jacques had her first credited big-screen role as Mrs Kenwick. While engaged at the Players' in June 1947, Jacques was introduced to the actor John Le Mesurier and the two began a relationship. Le Mesurier was married but estranged from his wife.