Lee officially joined the cast of MadTV in 2001 as a feature performer for the seventh season. He was promoted to a repertory performer status the following season, and has stayed there since.

Lee created many characters on the show, including Bae Sung, Hideki the "Average Asian" (an Asian American who is constantly being pestered by others who stereotype him based on his ethnicity), Tank (an overachieving import tuner street racer who uses his "ricer" Daewoo to pick up girls), and the Blind Kung-Fu Master (a blind martial arts master who usually fails his missions).

Lee is frequently called to perform female characters, which has become a huge running gag on the show. In recent seasons, one of his most frequent sketches is the one inspired by the TV show 24, in which he details what he does over the course of a day.

Another recurring gag is that he is in love with the female cast members, most prominently Arden Myrin and Crista Flanagan. In various skits, he is se