Southampton manager Alan Pardew was pleased to have won the race to sign Plymouth Argyle winger Jason Puncheon before the transfer window slammed shut.
The 23-year-old has signed a three-and-a-half-year contract at St Mary's, having spent most of the last 18 months on loan at MK Dons.
He has scored seven times this season, including one for the Dons in their 3-1 defeat on the south coast in late October.
Pardew told the club's official website: "He is a bit of a maverick footballer and I think the side could do with a bit of individual flair which he brings.
"He will help us control games from either the wide or central areas as he can play anywhere across the midfield and he gives us real competition in an area that I felt we needed to strengthen."