Lee Sang-yoon got his start in the entertainment industry in 2005 through a commercial for a beer brand. He then debuted as an actor in 2007, making appearances in several films and TV series. In 2010, he became part of MBC’s My Happy Home, which won him Best New Actor at the MBC Drama Awards. His career breakthrough came in 2012 when he starred in the hit KBS2 drama My Daughter, Seo-young, opposite Lee Bo-young. His work in the series scored him numerous acting nominations, including one for Best Actor at the 49th Baeksang Arts Awards. In 2013, he was nominated for an Excellence Award at the MBC Drama Awards for his performance in the sageuk Goddess of Fire. In 2014, He acted alongside Gu Hye-sun in SBS’s Angel Eyes, which earned him another Excellence Award at the SBS Drama Awards. In 2016, he joined Kang Ye-won in the mystery thriller film Insane, which gave him Best New Actor nominations at the 37th Blue Dragon Film Awards and the 53rd Grand Bell Awards. In 2016, he took home an Excellence Award at the KBS Drama Awards for On the Way to the Airport. In 2019, he received another Excellence Award at the SBS Drama Awards for VIP. In 2021, he was paired with Honey Lee in the SBS series One the Woman, which won him a Top Excellence Award at the SBS Drama Awards.

Lee Sang-yoon obtained a degree in physics from the Seoul National University. He previously dated actress Nam Sang-mi, who he worked with in the 2010 SBS series Life Is Beautiful. He was also in a relationship with singer-actress UEE.