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 SM Entertainment at the age of 11 through SM 2000 Casting System. Hyoyeon said that her reason was her mother bringing her to the offices of S. M. Entertainment in the hopes of meeting H.O.T. She then danced in her 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 #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.
She received dance instruction from the Electric Boogaloos and top choreographers such as Kim Hye-rang, Poppin Seen, Kwang Hoo (aka Crazy Monkey), Poppin DS, Kwon Seok-jin (aka Locking Khan) and Black Beat's Shim Jae-won. She also worked with one of Justin Timberlake's choreographers and a few foreign teachers.
Before debuting with Girls' Generation, she was BoA's silhouette dancer during a performance at M.net KM Music Festival 2005. In 2007, she teamed up with Jae Won for a dance collaboration to "Anonymous".

On March 7, 2010 she played a cameo role on SBS Oh! My Lady starring Choi Siwon and Chae Rim with fellow members Jessica and Sooyoung.
On October 17th, 2011 it was confirmed that Hyoyeon would be joining for the second season of Invincible Youth, a Korean reality show alongside with 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 MBC‘s Dancing with the Stars season 2, which aired its first episode on April 27th. Hyoyeon and her partner ended up winning second place.
In July 2012, Hyoyeon with fellow member Seohyun were featured in the August issue of Nylon, a fashion and pop culture magazine. To promote the upcoming release, the magazine recently 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 & fashion look book, ‘o/1 Creative Book‘.The first issue of “0/1creativebook”, featuring Hyoyeon, will be released on October 31. Hyoyeon becomes the first cover girl of newly-launched beauty fashion book, ’0/1 creativebook (Zero One creativebook)’! In the first issue of the book, Hyo-yeon is the only celebrity selected to model for the fashion book.
Hyoyeon is currently taking part as a member of SM Entertainment‘s new ‘Younique‘ dance unit which has partnered up with Hyundai to release their ‘PYL Younique Album‘ Edit Biography