Kang became a member of CNBLUE in 2009. The group debuted in Japan with the mini album Now or Never on August 19, 2009 with an indie label AI Entertainment. They officially debuted in Korea in 2010 with the mini album Bluetory, and the title track “I’m a Loner” became an instant hit in Korea.

In 2010, Kang began his acting career in an omnibus film Acoustic alongside his fellow CNBLUE member Lee Jong-hyun. He then made his small-screen debut in the SBS drama It’s Okay, Daddy’s Girl.

In 2011, he was cast in MBC’s youth melodrama Heartstrings, which stars fellow CNBLUE member Jung Yong-hwa. He sang an OST for the drama, titled “Star”.

In 2012, he starred in KBS’s weekend family drama My Husband Got a Family, and gained recognition for his role as a playboy. The series topped the weekly ratings chart for 25 consecutive weeks and reached a ratings peak of 45.8 percent (TNmS) and 52.3 percent (AGB Nielsen), making it the highest rated Korean drama in 2012.

In 2015, Kang became a fixed cast of KBS’s reality-variety show Brave Family, and became a host of JTBC’s show Mum is Watching.

After a three-year hiatus, Kang made his television comeback in SBS’s musical drama Entertainer in 2016, for which he won an Excellence Award at the SBS Drama Awards. The same year, he became a host of KBS’s live music show Music Bank with Laboum’s Solbin from July 2016 to November 2016.

In 2017, Kang was cast in his first lead role, playing a doctor in MBC’s medical drama Hospital Ship.

In 2018, Kang had a supporting role in the period comedy film, The Princess and the Matchmaker. The film was shot back in 2015.

Kang enlisted in his military service on July 31, 2018.

In 2019, Kang released two Japanese singles, Moontalk and On the Cheek, on January 7 and February 14, respectively. He dropped the album containing these two singles along with three more Japanese tracks on March 13.

On April 6, 2019, it was reported that Kang donated 10 million won to the victims of forest fires in Goseong County and Sokcho in Gangwon Province. According to Hope Bridge National Disaster Relief Association, the donation will be used for the recovery of the damaged areas.