Janssen also studied writing and literature at Columbia University before moving to Los Angeles to establish her acting career.
Janssen played superheroine Dr. Jean Grey/Phoenix in X-Men, X2 and X-Men: The Last Stand. She won a Saturn Award for the role in X-Men: The Last Stand. She also starred in the movies Lord of Illusions, The Faculty, House on Haunted Hill, I Spy, Rounders, Deep Rising and Hide and Seek. In addition, Janssen had a prominent role in the second season of the popular TV show, Nip/Tuck, as the seductive and manipulative transsexual life coach, Ava Moore.
Janssen tried to fight against typecasting by appearing in Woody Allen's Celebrity, Robert Altman's The Gingerbread Man, John Irvin's City of Industry and Ted Demme's Monument Ave. She was awarded the Special Jury Best Actress Award at the 2007 Hamptons International Film Festival for her role as a female pool hustler in Chris Eigeman's Turn the River.
In 2003, Janssen was awarded the International Star of the Year. In 2004, she won the Hollywood Life Breakthrough Artist of the Year for her work on Nip/Tuck. In 2006, the Hamptons International Film Festival awarded her with the Golden Starfish Award for career achievement in acting.
Janssen provides the Dutch-language narration for the Studio Tram Tour at all Disney parks.
On January 28, 2008, Janssen was appointed a United Nations Goodwill Ambassador for Integrity at the Second Conference of the States Parties to the United Nations Convention against Corruption, held in Nusa Dua, Bali.
|Year||Film||Role||Notes and Awards|
|1992||Star Trek: The Next Generation (TV series)||Kamala|
|Fathers & Sons||Kyle Christian|
|1994||The Untouchables (TV series)||Cleo|
|Melrose Place (TV series)||Diane Adamson|
|Model by Day (TV movie)||Lady X|
|Relentless IV: Ashes to Ashes||Dr. Sara Lee Jaffee|
|Lord of Illusions||Dorothea Swann|
|1997||City of Industry||Rachel Montana|
|The Gingerbread Man||Leeanne Magruder|
|Deep Rising||Trillian St. James|
|The Adventures of Sebastian Cole||Fiona|
|The Faculty||Miss Elizabeth Burke|
|1999||House on Haunted Hill||Evelyn Stockard-Price|
|2000||Love & Sex||Kate Welles|
|Ally McBeal (TV series)||Jamie|
|Don't Say a Word||Aggie Conrad|
|2002||I Spy||Special Agent Rachel Wright|
|2004||Nip/Tuck (TV series)||Ava Moore|
|2005||Hide and Seek||Katherine|
|2006||X-Men: The Last Stand||Jean Grey/Phoenix||Won - Saturn Award for Best Supporting Actress|
|The Treatment||Allegra Marshall|
|2007||The Ten||Gretchen Reigert|
|Turn the River||Kailey Sullivan|
|Winters (TV series)||Christie Winters|
|2008||The Wackness||Kristen Squires|
|100 Feet||Marnie Watson|
|Queen B||Havilland Winters||In negotiations|
|2009||The Possibility of Fireflies||Susanna Roma||Attached|
|The Finest||Gail/ G-Woman||Attached|