In 1999, together with Junsu he auditioned for SM Entertainment through the company’s Starlight Casting System at age 13. However he failed the audition in 1999 and entered again the following year and got in as a trainee. He began training in singing, dancing, acting, and had brief Mandarin Chinese language courses. He was also scouted with an interview offer from a top modelling agency in Seoul, yet declined due to contract issues. In the midst of trainee life in 2000, he reached SM’s master dance class and won the Goyang citywide dance competition in 2000. In 2002, Eunhyuk, Kim Junsu, and another trainee Sungmin were placed in a project R&B group. A year later, the group along with three future members from TRAX (Jay Kim, No Minwoo, Kang Jungwoo) made a brief appearance in a show called Heejun vs. Kangta, Battle of the Century: Pop vs. Rock, in which Moon Hee-joon and Kangta taught them techniques on different types of singing. In 2003 the trio disbanded when Junsu went on to debut as a member of TVXQ. Eunhyuk and Sungmin were then placed in another project group with ten other male trainees, Super Junior 05, the first generation of rotational boy band Super Junior.

Eunhyuk officially debuted as part of 12-member project group Super Junior 05 on 6 November 2005 on SBS’s music programme Popular Songs, where the group performed their first single, “Twins (Knock Out)”. Their debut album SuperJunior05 (Twins) was released a month later on 5 December 2005 and debuted at #3 on the monthly MIAK K-pop album charts.

In March 2006, SM Entertainment began to recruit new members for the next Super Junior generation. However, plans changed and the company declared a halt in forming future Super Junior generations. Following the addition of thirteenth member Kyuhyun, the group dropped the suffix “05” and became officially credited as Super Junior. The re-polished group’s first CD single “U” was released on 7 June 2006, which was their most successful single until the release of “Sorry, Sorry” in March 2009. Through their first official album, Eunhyuk helped produce as a lyricist and wrote the rap lyrics for a majority of Super Junior’s songs. The rap lyrics to “Show Me Your Love” from the winter single with TVXQ was written by him, along with Heechul and Shindong, and “One Love”, which became his solo performance in Super Junior’s first concert, Super Show.

Eunhyuk was partnered with bandmate Leeteuk as radio DJs for KBS Super Junior’s Kiss The Radio (aka SUKIRA) starting on 21 August 2006. With the exception of four months from March to June 2011, where bandmate Yesung temporarily replaced Eunhyuk, while he was away on promotional activities for Super Junior-M’s third EP Perfection.

Eunhyuk replaced Kangin as MC on Mnet’s music programme M! Countdown in late 2006. He hosted with bandmates Leeteuk and Shindong for two years and four months. In February 2007, Eunhyuk was placed in the trot-singing sub group Super Junior-T and released the single Rokkugo. A year later, he became a member of Super Junior-H.

On 19 April 2007, almost two months after Super Junior-T’s release of their first single “Rokuko”, Eunhyuk was involved in a car accident, along with Shindong, Leeteuk, Kyuhyun, and two managers, when returning home following a recording of the radio show Super Junior Kiss the Radio. While they were on the highway, the front left tire burst as the driver was switching lanes and the van ran into the guard rail/median on the driver’s side and skidded for about 30 metres. At some point, the momentum caused the van to flip over on its right side. While Shindong and Eunhyuk suffered minor injuries, Leeteuk and Kyuhyun sustained more serious injuries, which required both to be hospitalized.

From 2009, along with Leeteuk and Shindong, Eunhyuk was cast as a panel for Star King. In the midst of Super Junior’s growing popularity through their 3rd studio album Sorry, Sorry, Eunhyuk became a variety member of Strong Heart, where they hosted special segment, Boom Academy with comedian Boom. He became a member on KBS’ Dream Team, an athletic competition show and guested on Intimate Note, Fantasy Couple, Miracle and Introduce The Star’s Friend. Super Junior’s prominence nationally and overseas lead them to their second concert tour, Super Show II and line-ups in 2009 Asia Song Festival, Dream Concert, and premium live events in Japan, Singapore, and Thailand. It was then that Sorry, Sorry became critically and commercially successful hit in Asia; the first occasion in which the group won top honor at all of the local end-of-the-year music awards.

On 26 February 2010, Eunhyuk was diagnosed with H1N1 influenza, but was set to appear as a guest at label mate Girls’ Generation’s Into the New World encore concert in Seoul, hence had to pull out and was replaced by bandmates Leeteuk and Heechul. Super Junior released their 4th studio album, Bonamana, with similar success in Korea, sweeping awards in music programs after the release date. Their follow-up song, Boom Boom, was choreographed by Eunhyuk and performed on music programs Inkigayo and Music Core. On October 8, 2010, the digital single ‘Angel’ for HARU OST was released, with Eunhyuk featuring a rap verse.

In 2011, Eunhyuk, along with Sungmin was placed two new members of Super Junior-M. On 27 September 2011, he along with Yesung and Shindong filled in for bandmate Heechul, who enlisted for mandatory military service on 1 September, during the performance on Music Bank and Show! Music Core of Kim Jang-hoon latest single, “Breakups are So Like Me”. Heechul is featured in the song and starred in the music video, which was completed the day before he enlisted. Mr. Simple, Super Junior’s award-winning 5th studio album, was promoted heavily with Eunhyuk participating in much of the album’s production through choreography, and rap lyrics for the track, Oops. The album sold over 500,000 units and won the Disk Daesang Award at the 26th Golden Disk Awards and 21st Seoul Music Awards, as well as Album of the year at the 13th Mnet Asian Music Awards. The album is listed as the 2nd best-selling album as of the year 2011.

In November, Eunhyuk made his musical theatre debut in Fame, where he played Tyrone Jackson, along with Tiffany of Girls’ Generation, Son Ho Young, Lina of The Grace and Kim Jung Mo of TRAX. It was on at the Woori Financial Art Hall from 25 November 2011 to 29 January 2012. It was announced on 30 November 2011 that after five years, he and Leeteuk would leave Super Junior’s Kiss the Radio and was replaced by fellow members, Sungmin and Ryeowook on 4 December 2011.

On 16 December 2011 Eunhyuk and Donghae released digital single Oppa, Oppa, where they first performed it at Super Junior’s Super Show 4 Seoul concert on 19 November 2011. This marks the first release of their collaborations. The single was also released in Japanese with an original Japanese music video on 4 April 2012. On the day of its release, it reached number two on Oricon Daily Chart with 42,114 copies sold. While also preparing for Super Junior’s first world tour Super Show 4, the pair held a fan meeting, Premium Mini Live Event, in support of the single on 11 April at Shibuya-AX, Tokyo.

In June 2012, Eunhyuk reunited with his Super Junior bandmates for their sixth studio album, Sexy, Free & Single released on 4 July. On 21 June 2012, the first teaser photo of Eunhyuk was released showing him in a white shirt, blue jeans, styled with a mullet-like hairstyle and blindfolded with white and pink flowers. In October SM Entertainment and Hyundai partnered up to release the “Maxstep” featuring Eunhyuk and other SM artists Super Junior-M’s Henry Lau, SHINee’s Lee Taemin, EXO-K’s Kai, EXO-M’s Luhan and Girl’s Generation’s Hyoyeon. The group became the official dance unit; Younique Unit. The official cover of Zedd’s Spectrum was released via SBS Gayo Daejeon held on December 29, 2012, with Eunhyuk featuring. The single was performed by the members of SM The Performance and also included Donghae, along with TVXQ’s Yunho, Shinee’s Taemin and Minho and EXO’s Kai and Lay.

On January 7, 2013, Super Junior-M released their second album, Break Down, along with the music video for the lead single of the same name. A press conference took place in Beijing on January 7. They promoted the album in China. After returning to Korea, Eunhyuk heavily participated in variety shows, Come to Play (놀러와) and Barefooted Friends. Because of conflicting schedules due to Super Show 5: World Tour, Eunhyuk withdrew from both programs. Super Junior held 28 shows in total from March 2013 to February 2014, and toured in North America, South America, Europe and Asia.

In the midst of concerts, Eunhyuk returned to the studio for album recording. He and Donghae released I Wanna Dance on June 19, 2013 in Japan. The single peaked at #3 on both the Gaon and Oricon charts. Still You, the follow-up single, was released on December 18, 2013. Donghae & Eunhyuk then debuted their first studio album, Ride Me, on February 26, 2014 under Avex Trax. The song became the main theme of the Japanese TV show, ‘Sukkiri’ (爽快情報バラエティー スッキリ!!).

Eunhyuk returned to Super Junior-M promotions via Swing. The EP consists of six songs, which were released for digital download on March 21, 2014 in China and Taiwan by S.M. Entertainment. The group released the album in Korean music sites, such as MelOn, genie, Naver music and more, on March 31, 2014, and promoted on Korean music programs.

The first Japanese tour for sub-group Donghae & Eunhyuk, Super Junior D&E The 1st Japan Tour, kicked off in Nagoya on March 4, 2014. After touring numerous cities, he participated in a dance project with Beat Burger, entitled “Beat Burger Project x Eunhyuk”. In August, the project released an official video, choreographed to Yoo Young Jin’s song “Mo Jazzy”.

In August 2014, it was announced that Eunhyuk and Super Junior would be making their comeback with the group’s seventh album, Mamacita which was released online on August 29 and in stores on September 1. On the album, Eunhyuk contributed choreography to their second lead single, ‘Shirt,’ which received praises from Allkpop, “The track is one of the most energetic on the album beyond the title track.” The group made their official comeback performance on the Korean music show Music Bank with the songs “Shirt” and “Mamacita” on August 29 and continued their promotions on Music Core, Inkigayo and M! Countdown while preparing for their new world tour Super Show 6 which would open on September 19 on Seoul.

In February 2015, Donghae & Eunhyuk first Korean album, The Beat Goes On was released on March 9, 2015. The album had seven tracks, including the title song, “Growing Pains”. On April 1, Donghae & Eunhyuk released first Japanese mini-EP called Present, which contained a total of eight songs including the lead title “Saturday Night”. The duo kicked off its concert tour “Super Junior D&E The 2nd Japan Tour” and “Super Junior-D&E Asia Tour” during April to August.

Super Junior special album, Devil was released on 16 July 2015 to celebrate the group’s 10th anniversary. Eunhyuk participated in writing lyrics for song, “Alright”.

On September 2, 2015, SM Entertainment announced that Eunhyuk enlisted for active duty military service on October 13, 2015.

Eunhyuk was discharged on July 12, 2017. After his discharge from his enlistment, Eunhyuk participated in the songs writing and composing for Super Junior’s 8th Album “Play”, which was released on the group’s 12th anniversary.

In November 2017, Eunhyuk and Donghae announced their comeback in Japan as the duo group Super Junior D&E.

Starting in January 2018, Eunhyuk and his Super Junior members started a new variety program called “Super Junior’s Super TV”.

On May 22, 2020, Super Junior held their press conference for their web reality show on V Live with Leeteuk as the main host. Fans were wondering why Eunhyuk was absent, and Shindong spoke up, saying, “Eunhyuk couldn’t come because of personal reasons.”