On April 11, 2011, WM Entertainment unveiled Lee as the fourth member to be revealed after the release of the news of B1A4 along with Jinyoung, Baro and Gongchan's pictures.
As one of the projects for the show, B1A4 filmed a music video for "Only Learnt The Bad Things (못된 것만 배워서).
In December, on the Kim Bum Ryong special, he (with Baro) took the trophy for the first time, performing "The Way to Live Like a Man".
Under "Flowering Silky Fowl" stage name he became the runner-up of the first generation and, as a result, gained more recognition for his vocal ability.
On episode 17 opening, Lee performed a special duet with his role model, Kim Yeon-woo, singing "Is It Still Beautiful?"
Throughout 2016 Lee made numerous appearances on singing competition shows: He returned to do a single performance on Immortal Songs alone, and later that year with B1A4 as a full group for the first time.
In October 2016, Lee debuted as a solo artist with extended play Stay As You Are, where he first took part in writing and composing songs.
He was appointed alongside Kim Yeon-woo, Jung Ae-ri, Jin Se-yeon, Jang Na-ra and Yoon Joo-sang.
[11] Later, he joined singer Kim Yeon-woo for a special performance in You Hee-yeol's Sketchbook, urging people to vote.
[12] In addition, a video of Kim and Lee performing a remake of the song "As One Says" was released by The National Election Commission.
A month later, on Summer Spent Together with Friends special, singing Yim Jae-beom's "Flight" as a duet with actor Ahn Se-ha, he took his forth trophy.
[20][21] In August 2018, Lee was cast to play in the musical "Iron Mask", taking the dual part of the twins Louis and Philippe.
[24] During April and May 2019, WM Entertainment announced Lee is preparing for his first solo comeback,[25] with his second EP to be released on June 3.
[28] On December 29, 2019, Lee received an Excellence Award for his work as a DJ in the radio show "Starry Night".
On May 27, 2020, "Lazy Me" was released,[31] the first song of what meant to be three part series of digital singles project called "생각집" (lit.
[33] On July 20, 2020, Lee released a remake of Saevom's "Slightly Tipsy" as a soundtrack to the popular webtoon She is My Type.