Lee's interest in acting was inspired by the 1999 Korean film Shiri, and he began to pursue roles in theater in hopes of becoming a movie star.

Lee made the decision to transfer to Dongguk as it was the alma mater of Choi Min-sik, an actor he admired.

[6] Lee Kyu-hyung began his acting career in the Seoul Metropolitan Police Agency's " Whistle Theater " whilst attending college and completing his mandatory military service.

[5] In 2017, he played the role of Yoon Se-won, chief of the prosecution's investigation team, in the tvN drama Stranger, raising his profile.

[1] Director Shin Won-ho and writer Lee Woo-jung asked him to audition for the role after seeing his performances in the play Come See Me and the musical Fan Letter.

[5] Many viewers connected to his portrayal of the role, showcasing both cute and serious sides of the character, and it led to an increase in popularity for the actor both in Korea and overseas.