In August 2019, Lee departed CNBLUE after the backlash over a private direct message towards a YouTuber, and amidst allegations of him viewing illicit videos and having inappropriate sexual conversations degrading women in the Jung Joon-young KakaoTalk chatrooms, a part of Burning Sun scandal.

He was an ulzzang at "BESTNINE" alongside Mblaq's Lee Joon, fellow member Jung Yong-hwa, and Block B's Jaehyo before debut.

Lee, together with Jung, composed many of the band's released songs, such as "Blind Love", "Lie", "Rain of Blessing", "Kimio", "My Miracle", "Come On", "No More", "These Days" etc., which all gained positive feedback.

"Get Away", one of his compositions, was used as the ending theme song for the Japanese broadcast of American TV series Gossip Girl.

[3] Lee released his first solo single "My Love" in 2012, as part of the soundtrack for SBS drama A Gentleman's Dignity, which he starred in.

[6] In December 2013, Lee and his fellow label-mate Juniel formed a duo called "Romantic J" and released a digital single album titled "Love Falls".

[11][12] In 2010, Lee made his acting debut in the omnibus film Acoustic alongside fellow member Kang Min-hyuk.

[16] In May 2015, Lee starred in the fantasy high-school drama Orange Marmalade, alongside labelmate Seolhyun from AOA, where he plays a vampire.

[17] He also joined the fourth season of the Korean reality show We Got Married, pairing with actress Gong Seung-yeon.

[21] In 2017, he starred in the teen drama Lingerie Girls’ Generation in which he played a former gangster of Daegu who turned to be a kindhearted local handy man.

[28][29][30] On March 15, 2019, Lee admitted that he watched sex videos shared by Jung and he had made disparaging remarks about the women filmed.

[31] In August 2019, Lee departed CNBLUE after the backlash over inappropriate messages he sent to a YouTuber, which brought renewed attention to the Burning Sun issue.