The 20-year-old has signed a three-year contract and joins the Black Cats for an undisclosed fee.
Sunderland boss Steve Bruce said: “The boy has been in fantastic form for both club and country as he was one of South Korea’s stand-out performers at the Asian Cup, so we are delighted to bring him to Sunderland.
“The Premier League is very different to the K-League so there is hard work ahead.
“But you just have to look at players like Park Ji-sung Park and Lee Chung-yong to see how well Korean players are adapting to its pace and physicality.”
