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.
On March 25, 2012, it was revealed that Hyoyeon would be making an appearance on the second season of Dancing with the Stars. Hyoyeon joined the cast of the second season of MBC's Dancing with the Stars, which aired its first episode on April 27. Hyoyeon and her partner ended up winning second place.
In July 2012, Hyoyeon and fellow member Seohyun were featured in the August issue of Nylon, a fashion and pop culture magazine. To promote the upcoming release, the magazine uploaded videos of Hyoyeon and Seohyun onto its YouTube channel. The clips show behind-the-scenes footage of the photoshoots Nylon did with the two.
On October 30, 2012, Hyoyeon posed for beauty and fashion look book, 0/1 creativebook. The first issue of 0/1 creativebook, featuring Hyoyeon, was released on October 31. In the first issue of the book, Hyoyeon is the only celebrity selected to model for the fashion book.
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 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 on Dancing 9, Mnet's global dance survival show. The two Girls' Generation members coached the show's contestants as "K-pop dance masters" alongside other notable stars.
In February 2014, Hyoyeon participated in the 13th Korean Council of Sport All National Skiing Competition which was held at Welli Hilli Park in Hoeongseonggun, Gangwondo on February 17. She competed in the skiing race for young women and ended up placing first with a gold medal.
On May 6, 2015 was revealed that Hyoyeon will have her own reality show on OnStyle called Hyoyeon's One Million Likes. The show will start airing in June.
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.