He developed an interest in acting during his participation in an English play, "The Sound of Music," in 6th grade at Jeongji Elementary School.

He won the election for this position after actively engaging with his peers by arriving at school 30 minutes early to perform songs on the guitar.

He impressed the audience with his rendition of Rain's dance in "Rainism," which he shared on platforms like Daum TV Pod, Pikicast, and YouTube.

[9] That same year, Lee also auditioned for and was cast in the musical Infinite Power, which was the directorial debut of actor Park Hee-soon.

"[10][11][12] In 2016, Lee and Kang Young-seok were both cast as Nathan Leopold in the Korean production of Stephen Dolginoff's musical "Thrill Me."

Lee, a newcomer to the production, aimed to portray Nathan as a mild-mannered, soft-spoken character with exceptional logic and quick thinking.

[28] In 2019, Lee appeared on stage as Elvis impersonator Casey with Park Eun-seok and Kang Young-seok in the musical The Legend of Georgia McBride.

[29][30] In the same year, Lee appeared on television as a villain in Special Labor Inspector and as baseball coach Yang Seung-yeop in When the Camellia Blooms.

Lee's performance won over the hearts of the audience with his unique 'nerd beauty' and solid acting skills, as he comically searched for the members of the D'Ysquith family one by one.

In May, he joined the cast of the KBS2 Monday-Tuesday drama Youth of May[36] as Lee Soo-chan, a determined individual balancing family responsibilities and running a business in 1980s Gwangju.

Lee Sang Yi's authentic portrayal received praise, exploring themes of love, family, and ambition.

[34] in the same year, in May 2021, Lee appeared on the variety show program Hangout with Yoo and debuted as a member of MSG Wannabe as part of the sub-unit JSDK.

[40] On November 24, 2021, Lee reprised his role as Ji Sung-hyun and became a virtual guide for Gongjin VR tour which build on the popularity of Hometown Cha-Cha-Cha and was were released through LG U+ XR platform U+DIVe.

Studio Dragon utilized its premium intellectual property to present virtual reality (VR) contents in partnership with Korea Tourism Organization and LG U+.

It depicts a story about three young people who set foot in the world of private loans in pursuit of money and get caught up in a huge force.

[45] He shared the role of William Shakespeare with Jung Moon-sung and Kim Sung-cheol in a triple cast.The play received favorable reviews and Lee's performance was praised by the critics and the audience.

[46] In 2024, Lee returned to the small screen in the romantic comedy No Gain No Love in a supporting role as the main character's boss, CEO Bok Gyu-heon.