The 29-year-old joins Southampton for an undisclosed fee and has signed a two-and-a-half-year contract with the club.
The striker has spent the first half o the season on loan at the club.
Guly told the club’s official website: “The football and the fans make me happy here and I’m very happy with the new contract.”
Boss Nigel Adkins added: “He’s grown stronger and become part of the team so we are delighted we’ve been able to secure him on a long-term deal.”
