Born in Holland on January 1, 1964, Janssen launched her lucrative modeling career at an early age. Moving to New York when she was barely out of her teens, she soon tired of the vacuous nature of modeling and enrolled at Columbia University, where she studied literature and creative writing. Janssen made her screen debut in the 1992 drama Fathers and Sons. Following the success of GoldenEye, the actress began finding steady screen work, appearing in such films as Robert Altman's The Gingerbread Man (1998), in which she played Kenneth Branagh's ex-wife; Woody Allen's Celebrity (1998), which cast her as Branagh's girlfriend; and Robert Rodriguez's The Faculty, in which Janssen's part was furthered by alien brainwashing, instead of Branagh.

After closing the century with another excursion into supernatural grotesqueries in the remake of The House on Haunted Hill (1999), Janssen began the 21st century on a somewhat more heroic note, playing one of the titular group of superheroes in Bryan Singer's adaptation of the popular comic book X-Men.