The former Reading defender has followed Adlene Guedioura and Danny Collins to the City Ground, leaving troubled Pompey with just five players
Nottingham Forest have completed the signing of Portsmouth defender Greg Halford, who becomes Sean O'Driscoll's third signing since succeeding Steve Cotterill as manager.
Halford has become the third player to leave Pompey this week, leaving the south coast side with only five players, as Michael Appleton trims his squad to keep the club alive.
Speaking about the move Halford told Forest's official website: "It's been a tough year but the administrator wanted us all out.
"Not knowing whether there was going to be a club was unsettling.
"This is the right time for me to be here. The facilities are great. I know the owners have big plans as well."
The club's administrator, Trevor Birch, was warned that Portsmouth could close next month unless senior players agree to move or can reach agreements over their salaries.
Fans have been urging the remaining players to negotiate with the administrators in order to save their club whilst former manager Harry Redknapp has also offered his help in a bid to save Portsmouth.