Kim Jonghyun was born and raised in Seoul and is the youngest, having an older sister. Apart from being a member of boyband SHINee, he was also a member of a project group, SM The Ballad, under SM Entertainment.
Jonghyun was discovered by his label company, SM Entertainment, at the "2005 S.M. Casting System" Before debuting, Jonghyun sang a duet, "Wrongly Given Love" (交错的爱), with Zhang Liyin for her debut Chinese album, I Will.
After training for three years at his label company SM Entertainment, Jonghyun became a member of the five member contemporary R&B and pop boy band, Shinee.
In November 2010, it was revealed by SM Entertainment that SHINee's Jonghyun along with TRAX’s Jay, Super Junior’s Kyuhyun, and rookie singer, Jino, have formed a project group, SM The Ballad, under their label.
In October 2010, Jonghyun was one of 20 idols from various South Korean groups that recorded the song, "Let's Go," for the purpose of increasing public participation in 2010 G-20 Seoul summit. He provided vocals along with label-mates Sungmin, Seohyun and Luna.
On October 26 2010, Jonghyun was confirmed to be dating an actress, Shin Se-kyeong.
On 18 December 2017 it was confirmed that Jonghyun had passed away. He was found unconcious in a rented studio apartment in Chengdam-dong, in southern Seoul, after his sister alerted the authorities as she had been afraid he would commit suicide after being sent texts such as "It has been really hard. Let me go. Tell me I did well. This is my last goodbye. On the way to the hospital, he had a cardiac arrest and was later pronounced deceased upon arrival. It is suspected as a suicide due to carbon monoxide poisoning as there was a pan of burned coal in the apartment, as well as all windows and doors locked.
As soon as the investigation, began, it ended when police confirmed his death as a suicide the next day. Jonghyun's funeral took place on the 21st of December 2017, with family, friends, fans, and colleagues in attendance.