2003–2010: Member of TVXQ In 2001, at fifteen years old, Kim auditioned for
S.M. Entertainment and was accepted into the agency. From 2003 to 2010, he was the lead vocalist of South Korean boy band
TVXQ. After TVXQ went on hiatus in early 2010, he and two other fellow band members
Yoochun and
Junsu formed a new trio boy group, initially known as JUNSU/JEJUNG/YUCHUN in Japan. Kim sang the solo track "Maze" for the fifth and final single of the TVXQ/Tohoshinki's Trick Project, "
Keyword/Maze". Jaejoong wrote and composed which was included on TVXQ/Tohoshinki's twenty-fifth single "Bolero/Kiss the Baby Sky/Wasurenaide." The song was also on their fourth Japanese album
The Secret Code, along with the songs "9095" and "9096" which were also composed by Kim. The song, "忘れないで" was used in a television advertisement for cosmetics in Japan. Apart from his activities as a member of TVXQ, he sang "Insa" (인사, Greeting) for the soundtrack of ''
A Millionaire's First Love (2006). Kim collaborated with The Grace for the Japanese version of their song "Just for One Day", which was featured on their fifth Japanese single and their debut album, Graceful 4 (2007). Kim sang "Love" for the soundtrack of the film Heaven's Postman'' (2009) in which he starred as the male lead.
2009–2012: Formation of JYJ advertisement in 2011 In 2009 Kim, Junsu and Yoochun, started a lawsuit against their agency,
SM Entertainment, and separated from TVXQ, soon founding their own band,
JYJ. On September 30, 2009, Kim and bandmate Yoochun released a self-composed single "
Colors (Melody and Harmony)/Shelter." The A-side track, Colors (Melody and Harmony), was used as the image song for
Hello Kitty's thirty-fifth anniversary. Jaejoong and Yoochun also participated in m-flo's album
m-flo TRIBUTE -maison de m-flo, singing the track "Been So Long". Their debut Japanese language
EP The... was released in September 2010, and their first concert DVD from
Tokyo Dome Thanksgiving Live in Dome both reached No. 1 on the Japanese
Oricon album and DVD charts. The group's English language debut album,
The Beginning was released in October 2010, featuring
Kanye West. In January 2011, they released a Korean EP,
Their Rooms "Our Story", with three of Kim's own compositions, "Pierrot" (), "Nine" and "I.D.S.". In April he toured Asia and North America with JYJ, and later South America and Europe. He was also stage director of the Asian leg of the tour. In September the band released a studio album called
In Heaven, which sold 350,000 copies and ranked first on the
Gaon charts. He composed two new songs for the album, "In Heaven" and "Get Out". Kim composed "In Heaven" in memory of his good friend,
Park Yong-ha, who committed suicide. Apart from his activities as a member of JYJ, he also sang "Found You" and "For you It's Separation, For me It's Waiting" for the soundtrack of the television drama
Sungkyunkwan Scandal (2010), "I'll Protect You" for
Protect the Boss (2011), and "Living Like A Dream" for
Dr. Jin (2012). The album debuted at the top of both the Hanteo and Gaon weekly charts in Korea. It was also met with resounding success throughout Asia, topping Taiwan's Five Music's Korean and Japanese music chart, Japan's Shinseido weekly chart and Yin Yue Tai's V chart for K-pop. It also topped the iTunes rock charts in nine countries. Additionally, the pre-released single "One Kiss" and lead single "Mine" topped both domestic charts and foreign charts, including a German Asian music chart. On January 26 and 27, Kim held two days of special concerts at the KINTEX Ilsan to celebrate the launch of the album, as well as his birthday. Kim then released a repackaged version of his album, titled
Y which consists of contains two additional tracks: "Only Love" and "Kiss B". The album was met with success and sold 50,000 copies upon release. His first full-length Korean solo album,
WWW was released on October 29, 2013. A single titled "Sunny Day" was released ahead of the album and topped the iTunes EP chart in Japan. A repackaged version of the album,
WWW: Remove Makeup was subsequently released in January 2014 and included the title track "Heaven", a pop ballad with label-mate
Gummy. To promote his first album, Kim embarked on his first Asia tour which traveled to regional countries like Japan, Taiwan and China. He sang "But I" () and "Coincidence" () for the drama
Triangle (2014) in which he also starred. In July 2014, as a member of JYJ, they would release their first studio album in three years,
Just Us. The band reached the music charts with the song, "Back Seat". Prior to his military enlistment in 2015, Kim recorded the songs for his second Korean solo album,
No.X, which was released on February 12, 2016. It topped iTunes charts of 39 countries around the world upon its release, and was named the most popular K-pop album in China for 2016. He completed his military service in December 2016 and returned to the entertainment industry with his acting performance in
Manhole (2017).
2018–2022: Solo albums Kim released his first Japanese single "Sign / Your Love" on June 27, 2018. On October 24, 2018, he released his second Japanese single, "Defiance" / "Lavender". Both singles would be certified gold (selling over 100,000 copies) by the
Recording Industry Association of Japan. He promoted the album in Japan during his tour entitled
The Jaejoong Arena Tour 2019 – Flawless Love. The album was awarded the Planning Award at the
61st Japan Record Awards and the "Best 3 Albums (Asia)" award at the 34th
Japan Gold Disc Award. Following the EP's release, the cities and dates for his Asia Tour 2020 was announced. However, the tour dates were postponed due to COVID-19 concerns. He released his third Japanese single on March 10, 2020, "Brava!! Brava!! Brava!!" which debuted at number one on the Oricon weekly chart. It was the opening theme song for
Smile Down the Runway. It was announced on August 30, 2020, that he would be singing the opening theme song for
Noblesse, entitled "BREAKING DAWN" which was written and produced by
Hyde. The song will have an English, Korean and Japanese version. On September 18, 2020, Kim released "Even If I Call You" for the
Mr. Heart (2020) web drama, marking his first Korean soundtrack performance in six years. He soon followed that Korean soundtrack performance with another as he released "Things We Should Love" for the soundtrack of the Korean drama
Private Lives on October 28, 2020. In April 2022, Kim resumed activities in Japan with a live concert for his Japanese fanclub. He released a duet theme song with
Kim Junsu, "六等星" for the television adaptation of the manga ''
Waru - Who said it's not cool to work?'' on April 13, 2022. On September 13, 2022, Kim released his first Korean full-length album in six years titled
Born Gene. His Asian Tour to promote the album includes stops in Seoul, Kuala Lumpur and Bangkok. On October 30, C-JeS Entertainment It was announced that Kim has urgently decided to cancel the Japan concert due to the aftermath of the
Itaewon Halloween crowd crush.
2023: Inkode agency In April 2023, C-Jes Studio announced that Kim's contract would expire on April 22. on May 4, 2023, he announced the creation of his own agency Inkode. Inkode would focus on producing new idols and managing Kim's activities, with Kim serving as the
CSO. Noh Hyun-tae, the former vice president of
Cube Entertainment, will serve as the
CEO. and the first episode featuring
Tablo of
Epik High aired on July 27, 2023.
2024–present: Formation of JX Kim released his fourth Korean album
Flower Garden in June 2024, celebrating his 20th anniversary as a musician. He also returned to acting after a seven-year break with
Bad Memory Eraser (2024) airing on
MBN. The group debuted on October 16, 2024, with their
eponymous extended play, in which Kim solely wrote one of the album's tracks "Goldilocks Water". On September 6, 2024, at 12 AM KST, the two remaining
JYJ members, Kim Jae-joong and
Xia Jun-su, unveiled a teaser for their continued collaborative venture,
JX—which stands for Jae Joong and XIA—, on their newly created joint social media account. The teaser features a voice-over narration by the duo, emphasising their longstanding support for each other amidst the challenges and hinting at a new chapter in their journey. Following the debut of the duo, the announcement of an upcoming concert in
KSPO Dome from November 8–10 was revealed. ==Acting career==