Lee began her career as part of South Korean pop girl group Fin.K.L. As the eldest member, she was the leader of the group. Lee was discovered while taking sticker pictures with her friends and was the last member to join Fin.K.L, just before their debut in January 1998. Fin.K.L debuted officially on May 22, 1998 with their first single "Blue Rain". The second release from their debut album, "To My Boyfriend", became the first of their multiple number one hits. Fin.K.L became one of the most popular and successful South Korean pop groups of all-time, rivaling fellow popular girl group S.E.S.

A year after Fin.K.L's fourth studio album Forever, her solo debut album was released in August 2003, entitled Stylish. The lead single "10 Minutes" became one of her signature hits and the singer nearly swept the Daesangs, the most prestigious South Korean music award, winning more than seven of them, including three of the four most prestigious Daesangs. Stylish sold 144,182 copies in South Korea alone, according to the Music Industry Association of Korea in 2003. Her popularity in her various activities eventually was dubbed as the "Hyori Syndrome" in South Korea, and the Korean Media nicknamed 2003 "The Year of Hyori" as she was rarely out of the news all year.

Since Fin.K.L's disbandment, Lee became known for her sex appeal. This image has allowed Lee to lend her face and image to advertising for various company endorsement deals, and in 2005 she was chosen in a consumer survey as the female entertainer with the strongest brand power. In late 2003, Lee signed an advertising contract with Samsung, for which she would make three musical commercials and songs for their Anycall cell phones, which became some of her most prominent commercials. The first commercial and song, "Anymotion", was released in early 2005, featuring Eric Mun from Shinhwa. In early 2006, the follow-up commercial "Anyclub" featuring Teddy Park from 1TYM was released in two parts; the music video starred Eric Mun and actor Kwon Sang-woo. The songs from the commercials served as singles for Lee in between her albums. The final commercial was released in December 2006, titled "Anystar" and differed from the first two in that it featured mostly dialogue. The commercial starred actor Lee Joon-gi and YG Family trainee Park Bom (2NE1). Her contract with Samsung ended in December 2007.

In February 2006, Lee released her follow-up album, Dark Angel. The first single, "Get Ya!", was accused of being plagiarized by the songwriters of Britney Spears' single "Do Somethin'".

In 2007, she starred in a commercial with Jessica Alba for South Korean cosmetics company Ĭsa Knox, which was shot in Vancouver, British Columbia, Canada. Lee also modeled for cosmetics company Biotherm (her contract ended in February 2007), and Black Bean Therapy, a health drink. She then signed with KB Card, and has starred in commercials along with Rain. She was a model for Calvin Klein Jeans, modeling for the "Pure Calvin" Collection. She was also briefly featured in a 2010 Adidas commercial.

Her third studio album, It's Hyorish, was released on July 14, 2008. "U-Go-Girl", the first single from the album, hit #1 on online and offline charts, including various television music shows.

In November 2009, her contract with Mnet Media was set to expire. Lee planned to sign a contract with Gil Entertainment (currently B2M Entertainment) and work with Gil Jong-hwa who had been Fin.K.L's co-manager and had worked with the group since its debut. However, her 2010 album was released under the label of Mnet Media.

Soon after the release of the album H-Logic, seven of its songs, composed by Bahnus, were accused of plagiarism (among the allegedly plagiarized songs was "Bring It Back," performed by Canadian girl group Cookie Couture). On June 21, 2010, Lee admitted that the plagiarism accusations against her album were true, saying she had been "deceived"; she temporarily stopped all her activities as a singer and suspended her TV appearances.

While on hiatus, Lee began to grow as a cultural influence. She wrote online columns for vernacular newspapers such as The Hankyoreh that mixed her thoughts on life and career with social commentary, and was well reviewed for her simple prose, humor and intelligence. She also became an increasing presence in the civic community, emerging as one of the country's most high-profile animals rights Activists. In 2011, Lee released two charity songs for donation to animal shelters, "Please Stay Behind" (Hangul: 남아 주세요; RR: Nama Juseyo) and "Remember" (Hangul: 기억해; RR: Gieokhae).

In a June 2012 poll by Panelnow, Lee was listed as one of "the socialtainers that best represents Korea" alongside male broadcaster Kim Je-dong, male singer Kim Jang-hoon, and Actress Kim Yeo-jin.

She married musician Lee Sang-soon, Guitarist of rock band "Roller Coaster," on September 1, 2013 at their vacation home on Mt. Halla in Jeju Island. Both of them are members of an animal rights group and began dating after they collaborated in July 2011 on a song that Lee recorded to support animal shelters.

When SsangYong Motor laid off workers in December 2014, Lee gave public support of the workers via Twitter, announcing that she wanted to see the new car Tivoli sell well so they would be hired again, adding that, if it happened, she would dance in front of the car in a bikini.

In February 2015, Lee's representatives announced that her contract with B2M Entertainment had expired in 2013. In May 2015, Lee announced that she closed her blog as well as her Twitter account. Along with shutting down her social media, she stopped all of her television activities. In October of that year, Lee's representative told media outlets that she would be taking a 2-year hiatus from her entertainment career, "in order to have time for herself."

In October 2016, Lee hinted at working on new music. In November, it was confirmed that Lee had signed with Kiwi Media Group with a new album due in 2017. In December, Lee made a return to social media with posts on Instagram.

On July 4, 2017, her sixth studio album, Black, was released alongside the rustic-themed official music video for the title track. The mature, experimental sound started with Monochrome continues as Lee wrote eight and composed nine of the ten album tracks.