Seohyun was born on June 28, 1991, in Seoul, South Korea. As an elementary school student,Seohyun was discovered by a talent staff while riding in a subway train, who encouraged her to audition for SM Entertainment. In 2003, Seohyun auditioned and joined the company under the SM Casting System. She is known for singing children's songs for her audition unlike other applicants who usually sing pop and dance songs. She attended Seoul Middle School and Daeyoung High School, then transferred to Jeonju Arts High School, from which she graduated on February 9, 2010. She currently attends Dongguk University with fellow Girls' Generation member, Yoona, majoring in acting. She is also an accomplished pianist and guitarist.
In 2010, Seohyun was appointed by the Seoul Metropolitan Office as Korea's Goodwill Ambassador for Student Fitness. In 2012, Seohyun was appointed as the Goodwill Ambassador for the United Nation 2012 Yeosu Expo. On October 11, 2011, Seohyun was inaugurated as a UNICEF envoy at Changseong-Dong, Seoul. In the past, Seohyun has worked with UNICEF for the “Help Children in Africa” project.