Having appeared on the Showtime-aired Roger Corman horror presentations "Not of This Earth" and "Bucket of Blood" in 1995, Coolidge made her big-screen debut in the inane courtroom comedy "Trial and Error", co-starring "Seinfeld" alum Michael Richards. Equally believable as a pampered princess or a frumpy manicurist, Coolidge appeared in films more frequently with several character parts in 1998, including roles in the children's comedy "Slappy and the Stinkers", and a cameo as a sexy traffic cop in "A Night at the Roxbury". She also continued television work, most notably in a recurring part on the animated series "King of the Hill" (Fox) from 1997-1999, and in the more adult comedy "Rude Awakening" (Showtime) in 1998.

Coolidge had her breakthrough role in the popular comedy "American Pie" (1999) playing a well-preserved, boozed-up mom who seduces her son's classmate with the admission that she likes her scotch and men the same way: aged eighteen years. Recreating the character with a larger part in the 2001 sequel, “American Pie 2”, wasn't the only time Coolidge played drunk and sultry. "Down to Earth", the 2001 remake of "Heaven Can Wait", co-starred the actress as the scheming wife of an elderly mogul, a gold-digging type she previously visited as a wealthy dog owner more enamored with the trainer than her husband in the improv-based comedy "Best in Show" (2000). As Betty, a mostly silent hairstylist in the warm "The Broken Hearts Club: A Romantic Comedy" (2000), Coolidge heard the confessions and life lessons of a group of gay friends; as the unlucky but good-natured manicurist Paulette in "Legally Blonde", she was a confidante to Elle Woods (Reese Witherspoon), a walking Malibu Barbie-cum-Harvard Law student.

With roles that showcased the actress' no-holds-barred approach to comedy and her vanity-free comfort with altering both her appearance and manner to be unappealing, Coolidge emerged as a valuable character player and gifted comedienne. Working steadily, she had a brief cameo in the fashion espionage spoof "Zoolander" (2001) and was featured in the police parody "Showtime" (2001) as well as co-starred in the Showtime-aired romantic comedy "Oooph!" (2001), which was set to debut in the 2001-2002 season. In 2003, Coolidge joined with former co-stars once again, as she briefly reprised her manicurist role in "Legally Blonde 2: Red, White and Blonde", and made another cameo as Stifler's mom in "American Wedding," followed by a turn as Hilary Duff's wicked stepmother in "A Cinderella Story" (2004).

Coolidge's pneumatic form graced several TV comedies as well, with major guest appearances on "Frasier," "Sex and the City", and "According to Jim." A 2003 stint on an episode of "Friends" brought her to the attention of the producers who, upon the show's finale, departed for the Matt LeBlanc spin-off "Joey" (NBC, 2004 - ), where she was cast in a semi-regular role as dim but sweet actor Joey Tribbiani's all-too-blunt Hollywood agent Bobbi. Coolidge was then underused in a brief role as a White-Faced Woman in the Jim Carrey vehicle, “Lemony Snicket’s A Series of Unfortunate Events” (2004), an adaptation of the popular series of children’s books. She then was the voice of Aunt Fanny in “Robots” (2005), the well-reviewed animated feature about a world inhabited by mechanical beings.