[5] Prior to his debut in Super Junior, Heechul began his acting career in 2005, starring in the second season of teen drama Sharp 2.

[11] Following that, he made a breakthrough in his television host career after appearing on the variety shows Knowing Bros and Weekly Idol in 2015 and 2016.

[22][23] He was cast and signed a contract with SM Entertainment in November 2002, becoming an official trainee and being trained in singing, acting, dancing, and other performing talents such as hosting and modeling.

[25] Heechul was later preparing to debut as the main vocalist of TraxX, but had frequent clashes and misunderstandings with the person in charge at SM at the time.

[34] Heechul officially debuted as part of the 12-member project group, Super Junior 05 on November 6, 2005, on SBS' music program Popular Songs, performing their first single, "Twins (Knock Out)".

[40][41] Heechul faced criticism from Super Junior's fans when his voice cracked while performing "U", which negatively affected him and made him want to quit singing.

[49][50] Moreover, he co-hosted SBS's weekly live music show Inkigayo as a substitute for Andy of Shinhwa, later going on to become a permanent host starting April 23, 2006.

[59] He played the role of Sonny in the musical Xanadu, the first production of SM Art Company, in rotation with his bandmate Kangin.

[8] He hosted SBS Power FM's Kim Heechul's Youngstreet, from March 29, 2010, until mid-2011, returning to being a radio DJ after a four-year break.

[75] In the same year, he formed a project group with label mate Jungmo of TraxX, called M&D ("Midnight and Dawn" or "Miari and Dangae-dong", after the members' hometowns).

[78] He served as a public service worker for 23 months after undergoing four weeks of basic training at the Nonsan military camp in South Chungcheong Province.

[87][86] Heechul chose Ssulzun, a debate program which discussed current issues that affect South Korea, as his comeback appearance after finishing military service in 2013.

[89] On December 11, 2013, Super Junior released their fifth official Japanese single, "Blue World", the group's first song involving Heechul after he came back from military service.

[90] He appeared on the second season of MBC's reality television program We Got Married: Global Edition in January 2014 as an on-screen couple with Taiwanese girl group member Puff Kuo[91] and My Tutor Friend with Jeong Jun-ha as well.

In March 2016, Heechul was confirmed to become a temporary host for Weekly Idol until October 5, replacing Jeong Hyeong-don[108][109][110] He released a duet with Wheein for SM Station on April 15.

[137] Min Kyung-hoon wrote the lyrics to "Falling Blossoms" with his Buzz bandmates Yoo Woo-hyun and Shin Joon-ki.

[139][140][141] Heechul's debut solo digital single "Old Movie", was released on April 24, 2019, topping the charts in seven different countries[142][143][144] He held his first talk show event on May 4 and 5, which sold out in one minute from the start of internet ticket booking.

[13] Heechul continued his TV personality career in 2020, appearing in Studio Music Hall,[153] Love of 7.7 Billion,[154] and 20th Century Hit Song.

[155][156] On May 10, he earned his first Baeksang Arts Awards nomination at 56th ceremony in the Best Male Variety Performer category for Knowing Bros.[157] On December 1, it was announced that Heechul would be filling in as a temporary MC for KBS2's Problem Child in House, in place of the program's regular MC Jung Hyung-don until February 16, when he returning to active promotions.

[164] His web drama with Moon Ga-young Recipe for Youth which was originally set to be released in 2016, officially premiere on March 14 via BbangyaTV.

[179] Originating from a string of posts on X (formerly Twitter) by Japanese users, the rumors later implicated Kim after private photos of the singer associating with one of the involved women were shared; in response, Kim denied that he had drunk or shared meals with any of the junior SM Entertainment artists outside of work on the fan-messaging app Dear U.

[182][183] An active lyricist, he has written several of Super Junior's songs, including "Show Me Your Love", "Oops", and "Lo Siento".

[187][188][189] In October 2020, Ko Seung Woo and Jeong Chong Myeong credited Heechul alongside IU and Suga, as part of the force driving malicious commenters away for good.

[214] On March 14, 2022, Kim made a donation ₩100 millions to Community Chest of Korea for Fruit of Love to help the victims of the massive wildfire that started in Uljin, Gyeongbuk and has spread to Samcheok, Gangwon.

[223] In April 2023, he was appointed as a public relations ambassador for the Green Tree Foundation, an NGO working to cure and prevent school violence.

[240] Later that year, he was chosen as the honorary tourism ambassador for Hoengseong beef in 17th International Exhibition of Food & Drink, Hotel, Restaurant & Foodservice Equipment, Supplies & Services or HOFEX 2017 in Hong Kong.

[256] On August 10, 2006, Heechul was involved in a car accident while heading back to Seoul from Mokpo after attending the funeral of fellow Super Junior member Donghae's father.

[267] Heechul is still receiving treatment, and can no longer dance on live stages, often only making sporadic appearances for the latter half of the songs.

[271] In March 2018, it was reported that Heechul would not be participating in music show performances of Super Junior's repackage album Replay due to health concerns, but would still take part in other promotions as normal.

[277] The label further clarified in March 2020 that although he may not be able to perform on stage, he is still participating in Super Junior albums and other content by recording, as well as taking part in activities such as jacket photoshoots and MV filming.