Kangin officially debut as part of 12-member project group Super Junior 05 on 6 November 2005 on SBS's music programme Popular Songs, performing 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.

Five days after Super Junior 05's debut performance, Kangin became the MC of Mnet's M!Countdown along with Leeteuk and Shindong. The trio stayed as the hosts throughout the remaining year until Kangin was replaced by Eunhyuk in mid-2006 due to his busy schedule for hosting EBS Reckless Radio and MBC's music program, Show! Music Core. Kangin left Reckless Radio in June 2007 to host MBC's Good Friend Radio with Cho Jungrin. In 2008, Kangin was chosen to take the role of 'Kang Soo' in the Korean language film, Hello, Schoolgirl.

In February 2007, he was placed in the trot-singing Super Junior-T. A year later, he became a member of Super Junior-H. Kangin's silver-screen debut was in the Super Junior film Attack on the Pin-Up Boys, premiered on 26 July 2007.

Kangin also became the television host for two of MBC's popular entertainment programs, Sunday Sunday Night Dong-An Club and Nothing is Impossible. For Mnet channel, Kangin starred in 'Band of Brothers 2008' with Heechul, Jay and Jungmo. For MTV channel, in 2008 Kangin was a MC for 'Class Up'. In 2008, Kangin was one of 4 MCs for SBS 'Change' variety show. From September 9 to November 9, 2008, Kangin, along with bandmate Heechul, debuted as musical actors through the musical, Xanadu. Xanadu was a 1980s musical film starring Gene Kelly and Olivia Newton-John. Xanadu has also been reproduced to a Broadway musical. Heechul and Kangin, along with Choi Sungwon, performed the same character, Sonny, according to their time slot, and auditions and casting picks will be chosen in a process through reality television.

On October 16, 2009 around 3am, Kangin collided into a parked taxi that held no one inside, and left the scene of the accident. Five hours later, Kangin turned himself in to the police. He was recorded to have a blood alcohol content of 0.082% when he arrived at the station. Then he failed to show up at the Seoul Gangnam Police Station at 2pm on the same day for further investigation and had to be called in the following day.

SM Entertainment and Kangin released an official public apology shortly after. All of Kangin's activities were cancelled by SM Entertainment until the end of the year due to Kangin's actions. A month later Kangin made an appearance in a new clothing company, SPAO's website. Netizens were enraged due to SM Entertainment's declaration of the suspension of Kangin's activities. It was later found out that the photos were taken prior to Kangin's DUI accident. On 13 January 2010, Kangin was summarily indicted for drunk driving hit-and-run and fined ₩8 million by the Seoul Central District Court.

In June, 2012, SM Entertainment announced that Kangin will rejoin Super Junior for the group's sixth album, Sexy, Free & Single which had released on July 1, 2012. This also mark the first time he has appeared with Super Junior in three years since October 2009. On 25 June his teaser photo was released showing a slim downed Kangin with a frosty look and a net-like veil over his head.

On May 24, 2016, Kangin was involved in another DUI hit-and-run incident, with a blood alcohol content of 0.05%. S.M. Entertainment has issued a statement, stating his Future activities are cancelled while he reflects on his actions. He enters the Seoul Central District Prosecutors' Office on June 15, 2016, to face questioning over causing a traffic accident while under the influence of alcohol. Prosecutors summarily indicted him on July 7. On September 7, 2016, Kangin was sentenced to pay a ₩7 million ($6,420) fine.