In 1993, Messing won praise for her acting in the pre-Broadway workshop production of Tony Kushner's play Angels in America: Perestroika. Subsequently, she appeared in several episodes of the television series NYPD Blue during 1994 and 1995. In 1995, Messing made her film debut in Alfonso Arau's A Walk in the Clouds playing the unfaithful wife of Keanu Reeves. This exposure led the Fox network to make her the co-star of the television sitcom, Ned and Stacey. The series lasted for two seasons, from 1995 to 1997. Messing appeared as Jerry Seinfeld's date in two episodes of the series Seinfeld: "The Wait Out" in 1996 and "The Yada Yada" in 1997. Messing turned down a starring role in another television sitcom to appear in Donald Margulies's two-character play Collected Stories, which opened at the Off-Broadway Manhattan Theater Club. She also co-starred in McHale's Navy in 1997.

In 1998, Messing played a lead role as the bio-anthropologist Sloan Parker on ABC's dramatic science fiction television series Prey. During this time her agent approached her with the pilot script for the television show Will & Grace. Messing was inclined to take some time off, but the script intrigued her, and she auditioned for the role of Grace Adler, beating out Nicollette Sheridan, who later guest-starred on the show as a romantic rival of Grace's. Will & Grace became a ratings success, and Messing gained renown.

In 2002, she was named one of the "50 Most Beautiful People in the World" by People Magazine. TV Guide picked her as its "Best Dressed Woman" in 2003. Messing was cast by director Woody Allen in a small role in his 2002 film Hollywood Ending. Her film roles since include a happily married but ill-fated wife in the supernatural thriller The Mothman Prophecies (2002) and a supporting role in Along Came Polly (2004). The Wedding Date (2005) was Messing's first leading role in a high-profile film. It received mixed reviews but performed fairly well at the box office. Messing was featured as a judge on the season finale of the second season of Bravo's reality show, Project Runway. She also starred in the television mini-series The Starter Wife, which was nominated for ten Emmy awards including one for Messing for Outstanding Lead Actress in a Miniseries or Movie. Messing reprised the role of Molly Kagan in a second season of ten episodes of The Starter Wife in 2008.

• "The Starter Wife" .... Molly Kagan (13 episodes, 2008)
       - Woman Over the Influence (2008) TV episode .... Molly Kagan
       - Her Old Man & The Sea (2008) TV episode .... Molly Kagan
       - Look Who's Stalking (2008) TV episode .... Molly Kagan
       - The French Disconnection (2008) TV episode .... Molly Kagan
       - The Ex-Files (2008) TV episode .... Molly Kagan
        (8 more)
• Nothing Like the Holidays (2008) .... Sarah Rodriguez
• The Women (2008/I) .... Edie Cohen
• "The Starter Wife" .... Molly Kagan (5 episodes, 2007)
       - Hour 6 (2007) TV episode .... Molly Kagan
       - Hour 5 (2007) TV episode .... Molly Kagan
       - Hour 4 (2007) TV episode .... Molly Kagan
       - Hour 3 (2007) TV episode .... Molly Kagan
       - Hour 1 (2007) TV episode .... Molly Kagan
• Lucky You (2007) .... Suzanne Offer
• Purple Violets (2007) .... Kate Scott
• Open Season (2006) (voice) .... Beth
• Will & Grace: Say Goodnight Gracie (2006) (TV) .... Grace Adler
• "Will & Grace" .... Grace Adler (187 episodes, 1998-2006)
       - The Finale (2006) TV episode .... Grace Adler
       - Whatever Happened to Baby Gin? (2006) TV episode .... Grace Adler
       - Partners 'n' Crime (2006) TV episode .... Grace Adler
       - The Mourning Son (2006) TV episode .... Grace Adler
       - Blanket Apology (2006) TV episode .... Grace Adler
        (182 more)
• The Wedding Date (2005) .... Kat Ellis
• Garfield (2004) (voice) .... Arlene
  ... aka Garfield: The Movie (USA: promotional title)
• Along Came Polly (2004) .... Lisa Kramer
• "King of the Hill" .... Mrs. Hilgren-Bronson, Jordan's Mom (1 episode, 2002)
       - Get Your Freak Off (2002) TV episode (voice) .... Mrs. Hilgren-Bronson, Jordan's Mom
• Hollywood Ending (2002) .... Lori
• The Mothman Prophecies (2002) .... Mary Klein