The group debuted in Japan with the mini album Now or Never on August 19, 2009, with an indie label AI Entertainment.

[7] In 2010, Kang began his acting career in an omnibus film Acoustic alongside his fellow CNBLUE member Lee Jong-hyun.

[10] In 2011, he was cast in MBC's youth melodrama Heartstrings, which stars fellow CNBLUE member Jung Yong-hwa.

[17] Kang continued to gain more popularity after starring in The Heirs (2013), a teen drama penned by Kim Eun-sook.

[27][28] In 2017, Kang was cast in his first lead role, playing a doctor in MBC's medical drama Hospital Ship.

[46] Kang has been discharged as of March 19, 2020, without returning to his base from his ETS leave according to the Ministry of National Defense's policy.

[47] 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.