Saints have quickly followed on from Tuesday’s deal for Spain international Juanmi to sign Soares on a four-year contract from Sporting CP.
The 23 year-old has recently returned from international duty with Portugal, lining up alongside José Fonte – who, like Soares, began his career with Sporting.
Executive Director of Football Les Reed commented: “Cédric represents a quality addition to our squad, and is another player with a desire and hunger to succeed.
“Like Juanmi, Cédric is a young player with international experience as well as exceptional talent and potential. He joined Sporting’s academy at the age of eight and progressed through to first-team football and international recognition – a pathway previously trodden by a number of our own homegrown stars.
“We have been following Cédric’s progress for some time and felt now was the time to make our move. While there was competition from other Premier League clubs we were confident we would prove to be an attractive option for such an ambitious player.
“We have now signed two exciting talents early in the window and will continue in our pursuit of Premier League success and our European journey.”
Soares added: “I joined this club because I believe we can do better and better every year.
“Everyone knows that the Premier League is a very, very good league – and maybe the best one in the world – so for me it’s a pleasure to be here, but even more of a pleasure to be in Southampton.
”Southampton is a big, big club in England and is very respected. It’s a club with a lot of history and, for me, it’s very important to play for a big club. I think this is a very good move.”