Kim So-eun began acting in 2004 with a small role in the film Two Guys. Her career breakthrough came in 2009 when she played the heroine’s best friend in the popular KBS2 series Boys Before Flower. She also had appearances in the 2009 dramas Iron Empress and The Man Who Can’t Get Married, which both aired on KBS2. Her work in the said projects scored her the Best New Actress citation at the KBS Drama Awards. In 2010, she bagged her first leading role in the KBS1 daily series Fine Windy Day, opposite Jin Yi-han. In 2012, she became part of MBC’s 50-episode sageuk The Horse Healer, which gave her the Best New Actress trophy at the MBC Drama Awards. In 2014, she was paired with Song Jae-rim in the fourth season of the MBC reality show We Got Married, which won them Best Couple at the MBC Entertainment Awards. She was also named New Star of the Year at the same awards ceremony. In 2016, she reunited with Song Jae-rim in the SBS family weekend drama Our Gap-soon, which earned her a Special Acting Award at the SBS Drama Awards.

Kim So-eun trained as an athletic skier when she was a child. She attended Chung-Ang University.