Four singles from the album were released, all of them hits. "Complicated" went to No. 1 in Australia while reaching No. 2 on the U.S. Hot 100, and was also one of the best-selling Canadian singles of 2002. "Sk8er Boi" reached the top ten in the U.S. and Australia and No. 1 in Canada, "I'm With You" reached the top five in the U.S., while "Losing Grip" reached No. 1 in Canada, the top ten in Taiwan, and the top twenty in Chile. The media have often compared Lavigne to Alanis Morissette (one of her favourite artists alongside Coldplay and The Goo Goo Dolls), who is also Canadian, as well as singer-songwriters such as Vanessa Carlton and Michelle Branch, who emerged at about the same time and were popularly credited, with Lavigne, as part of a trend towards more creativity in the teen pop-music market.
Lavigne was named "Best New Artist" at the 2002 MTV Video Music Awards, won four Juno Awards in 2003 (out of six nominations), a World Music Award for World's Best-Selling Canadian Singer, and was nominated for eight Grammy Awards.
Lavigne's second album, Under My Skin, was released on May 25, 2004 in the U.S. It debut at No. 1 in U.S.A, U.K., Germany, Japan, Australia, Canada, Spain, Ireland, Thailand, Korea and Hong Kong and sold more than 380,000 copies in U.S.A in it's first week. . Lavigne wrote most of the album with Canadian singer-songwriter Chantal Kreviazuk, though some tracks were co-written by Lavigne and Ben Moody (formerly of Evanescence), Butch Walker of Marvelous 3, and the rest with her former lead guitarist Evan Taubenfeld. Kreviazuk's husband, Our Lady Peace frontman Raine Maida, co-produced the album with Butch Walker and Don Gilmore.
Lead single "Don't Tell Me" went to No. 1 in Argentina, top five in the U.K. and Canada, and top ten in Australia and Brazil. "My Happy Ending" reached the top ten in the U.S., and was her third-biggest hit to date there, but third single "Nobody's Home" did not make the top forty, though it reached the number one spot in Canada. The final single from the album, "He Wasn't", reached No. 1 in Canada, making the song her eighth No. 1 release since "Complicated", but failed to make the UK top twenty and was not released in the U.S.
Lavigne won two World Music Awards in 2004 for World's Best Pop/Rock Artist and World's Best-Selling Canadian Artist. She received five Juno Award nominations in 2005, picking up three, including Fan Choice Award, Artist of the Year and Pop Album of the Year. She also won the award for Favourite Female Singer at the eighteenth Annual Nickelodeon Kids' Choice Awards.
Lavigne co-wrote "Breakaway", which was recorded by Kelly Clarkson for the soundtrack to the film The Princess Diaries 2: Royal Engagement (2004) and was later included on Clarkson's second album, Breakaway, being released as the album's first single. It went on to peak at No. 6 in the US and provided Clarkson with a substantial hit.
Lavigne is to make her film debut in the animated film Over the Hedge, which is based on the comic strip of same name, alongside William Shatner, Bruce Willis and Gary Shandling. She is also acting in the Richard Gere film The Flock,  and her third project is Fast Food Nation, based on her favourite book. Her co-stars in the film include Patricia Arquette, Bobby Cannavale, Ethan Hawke and Greg Kinnear. 
In January 2006, Lavigne signed a contract with Ford Models.. She is appearing on the February edition of Harpers Bazaar Fashion Magazine with a new look.  Her third album is supposed to be released in November of 2006. Like her previous album, it should include collaborations with Kreviazuk and Maida.
Lavigne's band currently includes Devin Bronson (lead guitar), Craig Wood (rhythm guitar), Charlie Moniz (bass) and Matt Brann (drums). Former members include Evan Taubenfeld (lead guitar, 2002 2004), Mark Spicoluk (bass, 2002) and Jesse Colburn (rhythm guitar, 2002 2003). In 2003, it was reported that Lavigne was romantically involved with Colburn. Lavigne is engaged to be married to Deryck Whibley of the pop punk band Sum 41, and Mark Spicoluk was a former member of that band.
Lavigne performed "Who Knows" at the closing ceremony of the 2006 Winter Olympics (Turin, Italy) for the eight minutes of the Vancouver 2010 portion.