Lee Jung-jin began his entertainment career as a model before making his acting debut in the 1998 SBS sitcom Soonpoong Clinic. He has since appeared in numerous television dramas such as KBS2’s April Kiss in 2004, SBS’s Love Story in Harvard in 2005, and MBC’s I Love You, Don’t Cry in 2008. He has also starred in several films such as 2004’s Once Upon a Time in High School and 2005’s Mapado. In 2012, he led director Kim Ki-duk’s Pieta, which won the Golden Lion top prize at the 69th Venice International Film Festival. It also received the Okgwan Order of Cultural Merit from the South Korean government at the 2012 Popular Culture & Art Awards. In 2013, he acted alongside Eugene in the MBC series Hundred Year Inheritance, which won him top acting trophies at that year’s MBC Drama Awards and Korea Drama Awards. In 2014, he was nominated for an Excellence Award at the SBS Drama Awards for his work in Temptation. In 2020, he joined the main cast of the SBS romantic fantasy series The King: Eternal Monarch, which gave him another Excellence Award nomination at the SBS Drama Awards.

Lee Jung-jin enlisted for his mandatory military service in February 2005. He previously dated former Nine Muses member Euaerin for nearly two years.