The 26-year-old arrives at St Mary's on a free transfer from Sanfrecce Hiroshima and he has penned a two-and-a-half year contract with the Saints.
Lee, who could make his debut in the FA Cup fourth-round trip to Millwall this weekend, said he was delighted to have secured the move.
In a statement on the club's official website, he said: "I am very excited to join Southampton. It has been a long process but I am now looking forward to joining my team-mates and playing football.
"I feel good and ready and so will await the call from the manager on when I can put on the red and white shirt. I want to help the team to great things, we all want to get to the Premier League and I am the same.
"I hope that I can show the fans that they can trust me to play my best for the club at all times."




 





