Lee Jung-shin joined the pop rock band CNBLUE in September 2009 as replacement for bassist Kwon Kwang-jin, who departed the group shortly after the release of their debut Japanese extended play Now or Never. In January 2010, CNBLUE made their Korean debut with the mini-album Bluetory, which produced the hit single I’m a Loner. In March 2010, they dropped their first Japanese studio album called Thank U. A year later, they released their debut Korean full-length album titled First Step, which featured the singles Intuition and Love Girl.

Lee Jung-shin made his acting debut in the 2012 KBS2 series My Daughter Seo-young. His performance in the drama earned him several Best New Actor nominations, including one from the 49th Baeksang Arts Awards. In 2013, he was cast as one of the main characters in the KBS2 sageuk Sword and Flower. In 2016, he starred in the tvN romantic comedy Cinderella and the Four Knights. In 2017, he joined the main cast of the SBS sageuk My Sassy Girl, which scored him a Best New Actor nomination at the SBS Drama Awards. In 2018, he led OCN’s Longing Heart.

Lee Jung-shin enlisted for his mandatory military service in July 2018 and was discharged in March 2020. He has a passion for photography, which he uses to cope with stress and also for charitable deeds.