He initially rose to fame as a member of South Korean duo UN debuting with the single Voice Mail in 2000.

After the duo disbanded in 2005, his fame increased as an actor starring in Princess Hours, a drama based on a manhwa.

However Kim Jeong-hoon made his major break through when he starred in the hit MBC drama Princess Hours alongside Yoon Eun-hye and Ju Ji-hoon.

In 2016, Kim was cast in the Chinese drama God of War, Zhao Yun along with Girls' Generation's YoonA.

Kim attended Seoul National University and took up Dentistry but decided to drop out to focus on his acting career.