2014–2019: Theater beginnings Following his mandatory military service as a duty police officer at the National Police Agency, Lee Sang-yi debuted in the musical
Grease in 2014. He subsequently appeared in various musicals, including
Runway Beat and Legendary Little Basketball Team. That same year, he was cast as Jang Seon-jae in the musical
Infinite Power, which marked actor
Park Hee-soon's directorial debut. Lee noted that Park, a former member of the Mokhwa theater company, directed with an emphasis on individual actor's strengths, stating, "Having been an actor himself, the director understands the actor's mindset better than anyone else." In 2016, Lee and Kang Young-seok were jointly cast as Nathan Leopold in the Korean production of Stephen Dolginoff's musical
Thrill Me. Lee's portrayal of Nathan emphasized a mild-mannered yet logically acute character. Directed by Park Ji-he, the production ran from February 19 to June 12, 2016, and Lee's performance garnered attention for its emotional intensity. In 2016, his stage roles also included Benny in
In the Heights and Baek-seok in
Me, Natasha, and the White Donkey. In 2017, Lee participated in the Mongni Music Drama Concert 2017 [Grown Up], which ran at KT&G Sangsang Art Hall from February 16 to 26. He dedicated five weeks to rehearsing choreography from the film
La La Land with Park Ji-eun; their dance cover was posted on YouTube in March 2017 and achieved widespread popularity. In April, Lee performed in the play
Crazy Kiss, followed by the Korean premiere of
Guards At The Taj! in August. Later that year, he made his television debut as Oh Dal-soo in the drama
Manhole and appeared as Oh Dong-hwan in the
Prison Playbook series in November. Despite his television appearances, he maintained his commitment to stage performances. and a co-starring role in ''Today's Show - Moving Day
. In 2019, Lee portrayed Elvis impersonator Casey in the musical The Legend of Georgia McBridealongside Park Eun-seok and Kang Young-seok. This musical, written by American playwright Matthew Lopez, had premiered in the United States in 2014. In the same year, Lee appeared on television as an antagonist in Special Labor Inspector
and as baseball coach Yang Seung-yeop in When the Camellia Blooms''.
2020–2022: Breakthrough roles and debut as singer In 2020, Lee starred in the 100-episode weekend drama
Once Again. He played Yoon Jae-seok, a dentist and the younger brother of Yoon Gyu-jin, portrayed by
Lee Sang-yeob. His romantic storyline with
Lee Cho-hee's character became a fan favorite, with their on-screen pairing affectionately known as the "Sadon Couple" or "national in-laws." This performance earned them the Best Couple Award at the
2020 KBS Drama Awards, where Lee also received the Best New Actor Award. The drama's success considerably boosted his public recognition. After a two-year hiatus from musical theater, Lee returned in February 2022 to perform in ''
A Gentleman's Guide to Love and Murder''. He took on the role of Monty Navarro, a character determined to become a count by eliminating eight heirs of the D'Ysquith family. Lee's portrayal, which blended comedic elements with solid acting, was well-received by audiences, who noted his "nerd beauty" and strong performance. Lee maintained a busy schedule in 2021. In May, he joined the cast of the KBS2 drama
Youth of May as Lee Soo-chan, a resolute individual managing family responsibilities and a business in 1980s
Gwangju. His authentic portrayal, which explored themes of love, family, and ambition amidst challenges, was critically praised. Also in May 2021, Lee appeared on the variety show
Hangout with Yoo and debuted as a member of
MSG Wannabe's sub-unit JSDK. For the drama, Lee covered the song "Love is Forgotten" by and contributed to the original soundtrack with his single "I Hope You're Happy," released on October 17, 2021. On November 24, 2021, leveraging the popularity of
Hometown Cha-Cha-Cha, Lee reprised his role as Ji Sung-hyun and became a virtual guide for Gongjin VR tour. This initiative, a collaboration between
Studio Dragon,
Korea Tourism Organization, and
LG U+, utilized LG U+'s XR platform U+DIVe to create virtual reality content aimed at promoting South Korean tourist destinations through drama content. In November 2021, Lee once again performed as Monty Navarro in the musical ''
A Gentleman's Guide to Love and Murder. Concurrently, he confirmed his appearance in the Netflix Original Series Bloodhounds,'' featuring on three young individuals entering the private loan world and encountering a formidable force. 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 critics and audience. In 2024, Lee returned to the small screen in the romantic comedy
No Gain No Love as CEO Bok Gyu-heon. The chaebol businessman posts negative comments about a romance novelist, portrayed by
Han Ji-hyeon, but later falls in love with her. The couple was such a hit that the creators added a two-episode spin-off titled
Spice Up Our Love (2023) starring Lee and Han as a couple trapped in a romance novel. He next starred as a former silver medalist
fencer in
JTBC’s action-comedy
Good Boy (2025) alongside
Park Bo-gum and directed by
Shim Na-yeon. In the second half of 2025, Lee reprised his role as William Shakespeare in the play
Shakespeare in Love. In 2026, he reunited with
Good Boy co-star Park Bo-gum to star in
TvN's television show
The Village Barber. For the show, Lee earned his National Technical Qualifications Certification as a
nail technician. ==Filmography==