Hyoyeon was born in Incheon, South Korea on September 22, 1989. She grew up with her parents and her younger brother, Kim Min-gu. She auditioned for S.M. Entertainment at the age of 11 through SM 2000 Casting System. Hyoyeon said she auditioned because her mother brought her to the offices of S.M. Entertainment in the hopes of meeting H.O.T. Hyoyeon then danced in an audition show. In 2004, along with Super Junior's Siwon, she was sent to study Chinese in Beijing. Hyoyeon was also picked as Korea's No. 1 idol dancer on Star News.
Hyoyeon's formal dance training started in elementary school. At her neighborhood's small hip-hop school, she learned hip hop, jazz and Latin dance. In 1999, she enrolled in Winners Dance School, a famous dance school in South Korea specializing in popping, locking, animation and various other hip-hop styles. At the school she met Miss A's Min, with whom she formed the dance team Little Winners (리틀위너스). The duo performed at various showcases and was spotlighted by HipHoper.com in 2004.
On October 17, 2011, it was confirmed that Hyoyeon would be joining the second season of Invincible Youth, a Korean reality show, alongside Sunny.
Hyoyeon joined the second season of Dancing with the Stars, which began airing April 27, 2012. Hyoyeon and her partner, Kim Hyung Seok, ended up winning second place.
In October 2012, Hyoyeon took part as a member of SM Entertainment's Younique dance unit which has partnered with Hyundai to release the single "Maxstep".
In May 2013, Hyoyeon was chosen as an Asian ambassador for the Hong Kong branch of Topshop.
On June 17, 2013, it was revealed that Yuri together with Hyoyeon and others would appear as coaches on Dancing 9.
On May 6, 2015, it was revealed that Hyoyeon will star in her own reality show on OnStyle called Hyoyeon's One Million Likes. The first episode premiered on June 11, 2015. 
On June 24, 2015, it was announced that Hyoyeon will be the first Girls' Generation member that will publish a book, titled Hyo Style. It is scheduled to publish on July 3, 2015. It will contain 142 pages and a DVD.
On April 3, 2014, it was announced that Hyoyeon had been dating writer Kim Jun Hyung, age 35, for two years. SM Entertainment confirmed that the two had been a couple, but broke up on April 1 following a controversial incident where she accidentally hit him and was reported to the police for assaulting him.