Police told Yonhap News Agency that the star was found unconscious at an apartment studio in souther Seoul, South Korea.
According to reports he was then transported to a nearby hospital under cardiac arrest, and received emergency CPR treatment but did not regain consciousness.
Jonghyun's cause of death is still unclear.
SHINee was formed in 2008 by the South Korean entertainment company SM Entertainment. The hugely successful boy band consisted of five members: Jonghyun, Onew, Key, Minho and Taemin.
They released six chart-topping albums in Korea and five in Japan, in addition to embarking on several world tours. Jonghyun launched a successful solo career in 2015 and collaborated with numerous other Korean artists.
Our thought's are with all of Jonghyun's family and friends during this difficult time.
This article originally appeared on New Idea.