With a video that was strangely provocative – although the teenaged Moore dressed conservative in comparison to her then teen pop competition, Britney Spears and Christina Aguilera – "Candy" launched her MTV career as well. Reaching platinum sales by 2000, Moore was now a fixture on MTV, guest-hosting the popular daily series "T.R.L." and starring in TV specials such as "Mandy's Spring Break Makeover." Noting the performer's charm, charisma and excellent screen presence, the network offered Moore her own series during the summer of 2000 – "The Mandy Moore Show," which resumed in the summer of 2001, retitled "Mandy.”

A star whose work crossed media lines from the beginning, Moore began working as a Neutrogena spokesperson soon after "Candy" was released, and in 2000, the home video "Magic Al and the Mind Factory" surfaced, a children's project she had filmed in 1998. 2001 saw the actress make her big screen debut – first, with a small voice role in "Dr. Dolittle 2" and next as a pivotal supporting player in the G-rated Garry Marshall comedy "The Princess Diaries." As the popular tormentor of unlikely princess Mia (Anne Hathaway), Moore set aside her sunshiny image to play your typical catty schoolgirl bully. Excited for the opportunity to work with legends Marshall and star Julie Andrews, Moore enjoyed an overwhelmingly positive reaction to her entry into film, including a rather warm critics' reception. It seemed of all her blonde pop stars peers – Aguilera, Spears and Jessica Simpson – only the newly brunette Moore had the chops to make it as a Hollywood actress.

As "The Princess Diaries" was set to open in 2001, Moore had just finished filming "A Walk to Remember" (2002), a period romance set in small town America that paired her quiet, good girl character opposite troubled popular boy Shane West in a syrupy but effective teen "Love Story"-type tale. The film was an unsuspected success. She also saw the release of a self-titled album that showed a more mature, musically experimental side to the singer, which spawned a hit single with the edgy beat-driven lead-off, "In My Pocket".

After her debut starring role drew respectable box office numbers, Moore was next cast as the lead in "How to Deal" (2003), playing a teen whose cynical views on romance – spurred by her splintered family's misadventures in love – is turned on its head when she falls in love for the first time. That film was followed by another musical release, “Coverage” (2003), in which Moore attempted to bring songs by Elton John, Todd Rundgren, Cat Stevens and other classic rock and pop artists to her generation of fans. She next played the rebellious, overprotected first daughter of the United States President who, on a road trip to escape constant surveillance, unknowingly falls for the undercover Secret Service agent assigned to shield her, in "Chasing Liberty" (2004).

After that conventionally mild crowd-pleaser, Moore co-starred in the sly indie comedy "Saved!" – easily her best film up to that time – and demonstrated a surprisingly convincing edgy side in her portrayal of Hilary Faye, an overzealous and self-righteous Christian school student who demonstrates a surprising degree of intolerance when her pregnant best friend refuses to be "saved." The actress' dramatic depths and improvisational abilities added layers of complexity to her character, which in another's hands would have been entirely unsympathetic. For “Racing Stripes” (2005), a family-friendly combination live-action and animated feature, Moore provided the voice of Sandy, a young horse who helps Stripes the zebra run his first race. In 2005, Moore continued to impress on screen, when she scored a winning recurring stint on the comedy series "Entourage" (HBO, 2004- ) playing herself, sort of, who is having a complicated romance with her co-star Vincent Chase (Adrian Grenier) while shooting a big screen superhero movie for director James Cameron. After appearing in the “American Idol” big screen spoof, “American Dreamz” (2006), Moore charmingly played Diane Keaton's daughter in the misbegotten comedy, "Because I Said So" (2007). Despite a post-“Saved!” line-up of feature film misfires, Moore delivered a one-two punch during the summer of 2007 – first, with the release of her first self-written album Wild Hope, followed by her appearance in the hotly anticipated romantic comedy, “License to Wed,” co-starring John Krasinski of “The Office” (NBC, 2005- ) fame and Robin Williams.