More memorable was her powerful starring turn in Bill Bennett's "Kiss or Kill" (1997) opposite fellow "Love and Other Catastrophes" co-star Matt Day. The two played con artist lovers on the run after their routine scheme turned sour, accidentally killing their intended robbery victim and ending up with a sordid videotape that incriminates a sports celebrity. O'Connor shone in the well-made character driven thriller, capably handling the emotionally demanding role of a calculating and cool but anxiety-ridden young woman who is scarred by her mother's brutal murder, which she witnessed as a young child. The following year, she was featured in Peter Duncan's odd "A Little Bit of Soul", playing a genetic researcher who is competing with her former lover for a grant from a wealthy high ranking politician who is also a practicing Satanist.

In 1999, O'Connor took on her first non-Australian film, starring as Fanny Price in Patricia Rozema's adaptation of "Mansfield Park". A somewhat revisionist take on Jane Austen's novel, the film presented O'Connor's character as a more interesting and likable character than she is in the text, with Rozema inserting some of Austen's own personality (from writings in letters and journals) into Fanny's character. Although vastly different from her previous work, the actress gave an admirably strong performance in the role, remaining true to the script while letting her own modern spark shine through. She deftly handled the more reined in emotions necessary to the film, and proved a magnetic screen presence alongside co-stars Embeth Davidtz, Jonny Lee Miller and Alessandro Nivola. O'Connor followed up this acclaimed performance with a role as a book lover who brings her passion into the real world thanks to a seductive young man (Stuart Townsend) who happens to be dating her sister (Kate Hudson) in the Dublin-set feature "About Adam" (2000) before starring as the conflicted title character in the 2000 BBC-1 production of the Flaubert classic "Madame Bovary". That same year she was featured in the more commercial "Bedazzled" with a pivotal supporting role as a dream girl so compelling that a man (Brendan Fraser) makes a deal with the devil (Elizabeth Hurley) in an effort to win her heart. In 2001, she raised her profile considerably putting aside the historical pieces that helped her garner the attention of director Steven Spielberg to take on a futuristic role in the director's futuristic "A.I. Artificial Intelligence", playing the conflicted mother of a robotic boy (Haley Joel Osment). Reteaming with Brendan Fraser, O'Connor starred as Maggie in the acclaimed West End production of "Cat on a Hot Tin Roof" in the fall of 2001 and returned to period costume as co-star of the legendary Oscar Wilde comedy "The Importance of Being Earnest" the next year, essaying the charming Gwendolyn Fairfax opposite Colin Firth's lovestruck Jack Worthing. Later in 2002 she was featured in John Woo's World War II actioner "Windtalkers" (filmed in 2000).