Kim So-yeon entered the entertainment industry in 1994 at 14 years old by joining a beauty contest without her parents’ permission. That same year, she made her acting debut in the SBS series Dinosaur Teacher, in which she was named Best Young Actress at the SBS Drama Awards. In 1995, she won another Best Young Actress trophy at the KBS Drama Awards for her appearances in Daughters of a Rich Family and episodes of Drama Game. In 2000, she was cast in the MBC series All About Eve, which recorded a peak viewership rating of 45.2 percent.

After a three-year break from acting, Kim So-yeon made a comeback in the MBC romantic drama Gourmet in 2008. Her work in the series earned her the Best Supporting Actress trophy at the MBC Drama Awards. In 2010, she starred in the big-budget MBC series Iris, which gave her a Best Actress for TV nomination at the 46th Baeksang Arts Awards. In 2016, she collected acting recognitions for the MBC family drama All’s Well With a Happy Home, including the Daesang at the 9th Korea Drama Awards. In 2018 and 2019, she picked up Excellence Awards for her performance in the dramas Secret Mother and Mother of Mine. In 2020, she became part of the megahit SBS drama Penthouse, which won her Best Actress for TV at the 57th Baeksang Arts Awards. The series was renewed for two more seasons due to its success.

In June 2017, Kim So-yeon married her All’s Well With a Happy Home co-star Lee Sang-woo.