Kyuhyun made his first appearance as a part of Super Junior in a news broadcast on May 23, 2006 when the group was introducing their new single, U. Kyuhyun made his debut performance on May 26, 2006 at SBS's I-Concert performing the new single "U", where it was also the group's first return performance as a permanent group. Towards the end of 2006, Kyuhyun, along with Yesung and Ryeowook, was placed in Super Junior's first subgroup, Super Junior-K.R.Y. The trio debuted on November 5, 2006 on KBS's Music Bank
In early 2008, Kyuhyun was placed in a second Super Junior subgroup, Super Junior-M. The subgroup specializes in singing Mandarin songs, including versions of Super Junior's Korean songs, bringing the K-pop influence over to the Chinese music industry. Super Junior-M is the first international music group in the Chinese music industry to have members of both Chinese and Korean descent. The 7-member group debuted in China on April 8, 2008 at the 8th Annual Music Chart Awards along with the release of their first single music video, "U".
Not long after Super Junior-M's debut, they became one of the most celebrated boy-bands in China. The band's popularity skyrocketed further after their highly anticipated Mini-album, "Super Girl" was released on September 2009.
SM The Ballad
It was revealed that Kyuhyun along with TRAX’s Jay, SHINee’s Jonghyun, and rookie singer Jino have formed a project group under their label.
SM The Ballad released their debut album, Miss You on November 29, 2010. They debuted on Inkigayo on November 28, 2010. In their debut album, Kyuhyun had his solo song, "Love Again"
From the 15th of December 2010 to mid-January 2011, he acted with Yoo Jun Sang, Im Ki Jun, Kim Mu Yul and Dana Hong in the musical The Three Musketeers at the Chungmu Art Hall. He won a Golden Ticket Musical Rising Star Award for his performance of the role of D'Artagnan
In 2009, for the promotions of Super Junior's third studio album Sorry Sorry, Kyuhyun performed as one of the lead vocalists and traveled with the other members to overseas events, including Jackie Chan's Bird Nest Concert on April 8, 2009 with Zhang Liyin. The album brought immense popularity to the group after their long hiatus, allowing Super Junior to appear regularly in several variety shows and endorsements. They also held their second official Asia Tour, Super Show II.
Kyuhyun featured on Yoo Youngsuk's 20th anniversary tribute album, singing his first solo: a remake of Yoo's hit song "7년간의 사랑" ("7 Years of Love"). He first performed the song on July 10, 2009 on Yoo Hee Yeol's Sketch Book, the episode airing 2 days later. The song was released as a digital single, and Yoo Youngsuk's album was available online on June 30, 2009, with all proceeds going to UNICEF.
He and bandmate Donghae performed a special song "Happy Bubble" for a facial wash product commercial "Happy Bath" with actress Han Ji Min. A full music video was released on August 19, 2009.
Kyuhyun, along with the rest of Super Junior-M, returned in September 2009 to China to promote their first mini-album: Super Girl.
On January 6, 2010, Kyuhyun released his solo song "Listen To You", it is the main theme song for Korean drama "Pasta". When the song was first released on the music site monkey3 (www.monkey3.co.kr), it garnered a lot of attention and reached #1 on the real time chart.
On August 5, 2010, Kyuhyun released his third solo song "희망은 잠들지 않는 꿈 (Hope, a dream that never sleeps)" as OST for popular TV drama 제빵왕 김탁구 (Baker King, Kim Tak Goo).
Aside from the official solo releases, Kyuhyun has also performed a variety of other songs such as "Believe", Qi Qin's "Won't Let My Tears Accompany Me Through The Night (不讓我的眼淚陪我過夜)", Nicholas Teo's "Tears of Polaris", Jam Hsiao's "Forgive Me" and "A Goose's Dream" with Jonghyun of SHINee. Kyuhyun also collaborated with The Grace in early 2008 to perform "하루만 (Just For One Day)" for The Grace's first album 한번 더, OK?, and along with fellow Super Junior member Ryeowook and labelmate TVXQ's Xiah and Changmin for the song 소원 (Wish), which appeared on TVXQ's repackaged version of Mirotic. During the SMTown Live '10 World Tours he sang the song "Call With My Heart" and "Way Back Into Love" with Girls' Generation's Seohyun