Duff recorded a cover of Brooke McClymont's "I Can't Wait" for the original television soundtrack for Lizzie McGuire in 2002 (see Lizzie McGuire (soundtrack)), and "The Tiki Tiki Tiki Room" for the first Disneymania compilation album.

Her first album was Santa Claus Lane (2002), a collection of Christmas songs which included duets with Lil' Romeo, Christina Milian, and her sister Haylie. Accompanied by the Disney Channel-only single "Tell Me a Story", it peaked well outside the top 100 on the U.S. Billboard 200 album chart, but eventually received a gold certification. The album's title track was included on the soundtrack to The Santa Clause 2 and another song, "What Christmas Should Be" was used in Cheaper by the Dozen. Duff sang several tracks for the soundtrack to The Lizzie McGuire Movie (see The Lizzie McGuire Movie (soundtrack)), including "Why Not", which became a modest top twenty hit in Australia.

Duff's second studio album, Metamorphosis (2003), included contributions by songwriter-producers such as The Matrix and reached number one on the U.S. and Canadian charts. It became one of the biggest selling albums of the year in the U.S. and has since gone to sell over 3.7 million copies. The lead single, "So Yesterday", was a top ten hit in several countries and its music video received heavy airplay on MTV, while "Come Clean" became Duff's first top forty U.S. hit and reached the top twenty elsewhere. The third single, "Little Voice", was not released in the U.S. and was a minor hit in Canada and Australia. In late 2003 Duff embarked on her first concert tour, the Metamorphosis Club Tour and later the Most Wanted tour. All shows on her tour were sold out, a feat neither Britney Spears nor Christina Aguilera achieved that year. She won the award for Best New Artist at the 2004 World Music Awards and Best Female Artist at the Kids Choice Awards of 2004.

The second Disneymania disc was released in January 2004 and contained a duet with her sister, "The Siamese Cat Song". Another song, "Circle of Life", featured Duff and other Disney Channel Stars. Duff and her sister recorded a cover of The Go-Gos' "Our Lips Are Sealed" for the soundtrack to A Cinderella Story, which included two other songs by Duff. The video for "Our Lips Are Sealed" was popular on MTV's TRL but the song itself failed to chart on the U.S. Billboard Hot 100.

Duff co-wrote several of the tracks on her third album, the self-titled Hilary Duff, which she had an edgier, rock feel than Metamorphosis. It was released on her seventeenth birthday (in September 2004) and debuted at number two in the U.S. and number one in Canada. The album has sold over 1.5 million copies in the U.S. to date,[15] but the single "Fly" failed to chart in the U.S. despite a popular video. Fly and "Someone's Watching over Me" reached the Australian top forty, but because the album was less successful than Metamorphosis, no other singles were released commercially. Duff then continued nine more months of the Most Wanted Tour.

Duff's fourth album, Most Wanted (2005), comprised her favorite tracks from her previous two albums, remixes, and new songs inspired by pop-rock musicians such as The Killers and Muse. Duff stated that it was not a greatest hits album, but that her label told her it was time to release a new album. She had more creative control over Most Wanted compared to her previous releases, co-writing and co-producing all of the new material with Joel Madden and his brother Benji, both of the band Good Charlotte. The lead single, "Wake Up", became Duff's highest debut on the Billboard Hot 100 and her highest peaking single in the U.S., and its video received heavy rotation on MTV. The video for the second single, "Beat of My Heart", was also popular, but the single itself did not chart in the U.S. The album itself debuted at number one on the Billboard 200 and became her third number-one debut in Canada. By March 2006, it had sold 1.3 million copies in the U.S. An Italy-only compilation, 4Ever, was released in 2006.

Duff recorded new songs for her Madonna produced film Material Girls, including a Timbaland-produced cover version of Madonna's "Material Girl" with her sister. According to Total Request Live, Duff's fourth studio album was to be released in the United States in February 2007 because of her commitment to the film Brand Hauser; it was later pushed back to April. Titled Dignity, it is preceded by the single "Play with Fire", which was released to U.S. radio in August 2006.

Duff has co-written material for the album with Kara DioGuardi, and she also worked with producer-songwriter Rhett Lawrence in Toronto, Canada. She said that compared to her previous music it would be "more dancey" and make use of more real instruments. "I don't know exactly how to explain what we're doing, but it's fun and funky and different, something new for me. It's really cool", she said. She has also described the album's sound as "a little less pop-rock and more electronic-sounding". The music video for Duff's second single, "With Love", is scheduled to premiere as part of TRL's Brand Spankin new music week on February 8th.[27] The music video for "With Love" has also been used as the commercial for Duff's first fragrance, With Love . . . Hilary Duff, which was lauched in September 2006. "With Love" was released on January 25, 2007 on radios when Duff was on air with Ryan Seacrest on Kiss FM. Hilary's fourth studio album will be titled Dignity. The following songs: "Play With Fire," "With Love", "Gypsy Woman", "Happy", "Where's Your Dignity?", "Stranger", "Danger", are so far confirmed to be included on the album. Dignity is said to show a more mature side of Duff. Hollywood Records is currently planning to release at least five singles from Dignity. It is included on Bill Lamb's Top 10 2007 Albums to Watch for at number 8. Duff has been working with some exciting producers and mixers such as Richard "Humpty" Vission, Tim and Bob, and Manny Marroquin. She also co-wrote all the songs on the album and it explores the themes of "living in Los Angeles" and "the suspect advances of an older man".