So Yi-hyun debuted as an actress in 2003 with the KBS1 series Yellow Handkerchief. That same year, she became part of SBS’s Punch, which won her the New Star Award at the SBS Drama Awards. Since then, she has appeared in numerous TV series such as 2004’s April Kiss and 2005’s Resurrection, which both aired on KBS2. In 2009, she played one of the main characters in the MBC family drama Assorted Gems. In 2013, she became an MC for the MBC entertainment news show Section TV, which gave her an Excellence Award at the MBC Entertainment Awards. She also acted alongside Taecyeon and Kim Jae-wook in the 2013 tvN melo-thriller Who Are You. In 2014, she joined the main cast of the SBS series Three Days, which earned her an Excellence Award at the SBS Drama Awards. In 2016, she took home another Excellence Award, this time at the KBS Drama Awards for the daily series Secrets of Women. In 2021, she starred in another KBS2 daily drama called Red Shoes, which scored her two acting trophies.

So Yi-hyun tied the knot with actor In Gyo-jin in October 2014. They were co-stars in several TV series such as SBS’s Ae-ja and Min-ja in 2008 and JTBC’s Happy Ending in 2012. They have two daughters together.