Lee Hong-ki debuted with F.T. Island a.k.a. Five Treasure Island in 2007 with the song Love Sick from their first studio album Cheerful Sensibility. The following year, the group dropped their debut Japanese extended play Prologue of F.T. Island: Soyogi, signaling their expansion into the Japanese market. In 2015, Lee Hong-ki made his solo debut with the release of his back-to-back Korean and Japanese albums titled FM302 and AM302, respectively.

Prior to becoming part of F.T. Island, Lee Hong-ki first debuted as a child actor in the 2002 KBS2 series Magic Kid Masuri. In 2009, he joined the main cast of the SBS idol-star drama You’re Beautiful, which won him the New Star Award at the SBS Drama Awards. In 2013, he made his big screen debut in the film Rockin’ on Heaven’s Door. In 2014, he starred in TV Chosun’s Hundred Year Bride and in SBS’s Modern Farmer. In 2017, he played one of the main characters in the tvN fantasy drama Hwayugi.

Lee Hong-ki enlisted for his mandatory military service in September 2019 and was discharged in April 2021. He dated his Modern Farmer co-star Han Bo-reum.