Hudson's breakthrough was as Penny Lane in Cameron Crowe's Almost Famous (2000), for which she won the Golden Globe Award for Best Supporting Actress and was nominated for an Academy Award for Best Supporting Actress. She had previously appeared in the lesser-known films Gossip, a teenage drama, and 200 Cigarettes, a New Year's-set comedy with a large cast of actors. Regarding her early career and success, Hudson has noted that she is a "hard worker" and did not want to be associated with her well-known parents, wishing to avoid the perception that she "rode on somebody's coattails".
In 2002, she starred in the remake of the historical romance The Four Feathers, a film which was not well received by critics or audiences. Her next film, the romantic comedy How to Lose a Guy in 10 Days, was a box office success, grossing over $100 million after its February 2003 release. Hudson subsequently appeared in several romantic comedies, including Alex and Emma and Raising Helen; the films met with varying degrees of success.
Hudson headlined a thriller called The Skeleton Key in 2005. The film, which had a production budget of $43 million, enjoyed box office success, grossing over $91.9 million worldwide ($47.9 million in North America). Her later film, a comedy titled You, Me and Dupree and co-starring Owen Wilson and Matt Dillon, grossed $21.5 million on its opening weekend of July 14, 2006.
In 2007, Hudson directed the short film Cutlass, one of Glamour magazine's "Reel Moments" based on readers' personal essays. Cutlass co-stars Kurt Russell, Dakota Fanning, Virginia Madsen, Chevy Chase and Kristen Stewart.
In 2008, she appeared in Fool's Gold, a romantic comedy released on February 8, and her second film to co-star Matthew McConaughey. She had been certified in scuba diving in the Great Barrier Reef for the movie's underwater scenes. Also the same year, she appeared in another romantic comedy, My Best Friend's Girl, which was released in September.
Hudson next appeared in the musical film Nine, alongside Daniel Day-Lewis, Marion Cotillard, Penélope Cruz, Nicole Kidman and Judi Dench. The film, directed by Rob Marshall, was released in December 2009. Hudson was critically acclaimed for her unknown dancing skills, showcased in a stylish 1960s inspired original piece called "Cinema Italiano", which was written specifically for the film and for Hudson's character.
She starred in the film adaptation of Jim Thompson's The Killer Inside Me. The film premiered on January 24, 2010, at the Sundance Film Festival.
In 2011, she played Darcy in Something Borrowed, based on Emily Giffin's novel of the same name.
In 2012, she made her first appearance on Glee as Cassandra July. Hudson's character is Rachel Berry's dance teacher at NYADA (New York Academy of the Dramatic Arts).