As an actor, Lee started his career by starring in children drama Magic Kid Masuri (2002).

He later successfully transitioned to adult role and participated in various television dramas, notably You're Beautiful (2009) and A Korean Odyssey (2017).

In 2008, he was offered the lead role in Master of Study, the Korean adaptation of Japanese drama Dragon Zakura.

Lee then played Lysander in a Korean musical theatre version of A Midsummer Night's Dream,[3] where he showcased his singing, acting and dancing skills.

In 2009, after a five-year break, he made his acting comeback and took the role of the quirky but loveable drummer Jeremy in You're Beautiful.

You're Beautiful recorded modest ratings in South Korea, but it became an international success and with it, Lee's worldwide popularity increased.

[6] This was followed by a 90-minute Korean-Japanese co-production titled Noriko Goes to Seoul, in which he played a young aspiring singer who meets an older woman (Takashima Reiko) who inspires him through hardships to achieve his dream.

[7] In June 2013, he made his big screen debut in the movie Rockin' on Heaven's Door (Korean title: Passionate Goodbye), with Baek Jin-hee, in which Lee portrayed as a rebellious music star who is sent to work in a hospice.

Impressed by his powerful vocal ability, a few music agents approached him, not wishing to waste his talent for singing.

Then-fledgling label company FNC Music signed Lee and fully trained him to become the lead singer of F.T.

In 2015, Lee announced through social media that he was working on both a Korean and Japanese album, which was released in November and December respectively.

The title song "Insensible" is a ballad track and it tells the sad story of a man who is unable to forget his previous love.

On the other hand, the music video for the lead single of the Japanese album AM302, "モノローグ (Monologue)", was published on November 11, 2015, on F.T.

On May 21, 2015, Dal Shabet's official YouTube channel uploaded a video titled "Joker" in Rock Version.

In recent years, Lee has also begun composing music, contributing the songs "Black Chocolate" and "Orange Sky" to F.T.

They met with 80 victims of the 2011 Tōhoku earthquake and tsunami, who were students and staff from Ogatsu Middle School in Ishinomaki, Miyagi Prefecture.