Kim Sang-joong debuted as a musical stage actor. In 1991, he landed his first film role in the movie Money, Money, Money. In 2000, he bagged an Excellence Award and the Big Star Award at the SBS Drama Awards for his work in Legends of Love and SWAT Police. In 2002, he received a Top Excellence Award at the KBS Drama Awards for the sageuk The Dawn of the Empire, where he portrayed King Gwangjong. In 2007, he played the role of a college professor having an affair with his wife’s friend in the SBS series My Man’s Woman. His performance in the drama earned him a Top Excellence Award at the inaugural Korea Drama Awards and an Excellence Award at the 2007 SBS Drama Awards. In 2012, he took home two acting trophies for the SBS action thriller The Chaser. In 2013 and 2014, he picked up back-to-back acting recognitions at the MBC Drama Awards for the dramas Gold Rainbow and A New Leaf. In 2017, he won two Daesangs for his work in the MBC sageuk Rebel: Thief Who Stole the People.

Kim Sang-joong has also been the host of the long-running SBS program Unanswered Questions since 2008. His hosting skills were recognized with an Achievement Award at the 2012 SBS Entertainment Awards. He also won the Best Performer trophy at the 41st Korea Broadcasting Awards in 2014 for his work in the program.

Kim Sang-joong tied the knot in 1991, but he and his wife divorced in 1999. They have a son.