Michelle Lynn Monaghan was born on March 23, 1976, in Winthrop, Iowa, to Sharon Hamel, a day care center owner, and Robert L. Monaghan, a factory worker and farmer, making her the youngest of three children and the only daughter.
Her ancestry is predominantly Irish and German.
After completing high school in Iowa, Monaghan pursued a three-year journalism course at Chicago's Columbia College.
To support her education, she took up modeling and eventually quit college in 1999 to work full-time as a fashion model in New York.
She traveled extensively, walking runways in Milan, Singapore, Tokyo, and Hong Kong, and appeared in numerous magazines and catalogs.
In 2000, Monaghan made her television debut in two episodes of Young Americans and later appeared in Law & Order: Special Victims Unit.
She made her film debut with a small role in Perfume in 2001.
Monaghan's breakthrough came in 2002 when she co-starred as Kimberly Woods in the TV series Boston Public for one season.
She then appeared in several supporting roles before starring alongside Robert Downey Jr. and Val Kilmer in the black comedy Kiss Kiss Bang Bang in 2005.
Later that year, Monaghan filmed Mission: Impossible III in China, Italy, and the United States, playing the female lead opposite Tom Cruise.
In August 2005, Monaghan married her long-time sweetheart, Peter White, a New York-based graphic designer, whom she met at a Manhattan party five years earlier in Sydney, Australia.