Hyun was born and raised in Seoul. He has two older brothers. He graduated from Chung-Ang University in 2004 where he majored in Theater Studies. Since 2009 he has been enrolled at the same university for a master's degree.
In August 2009 Hyun confirmed that he was dating Song Hye-kyo, his co-star in Worlds Within. In March 2011, hours after Hyun's military enlistment, his and Song's agencies confirmed speculation that the couple had broken up. According to the joint press release, "Both have been very busy shooting films and dramas both in and out of Korea, which inevitably caused them to grow apart. Excessive media scrutiny of their relationship put extra strain on them, and rumors of their split were a source of great stress. They did not have enough time to overcome these obstacles and the distance between them grew." With rumors of their separation circulating since the end of 2010, the agencies said the two split up in early 2011 but wanted to keep it secret for the time being "because neither of them wanted the public attention to be directed on their split instead of their professional work. Hyun also did not want a personal issue to interfere with his last days with his fans before starting his military service.