Millwall stopper joined Pompey on a season-long loan in July 2016.
The veteran Irishman has made 339 appearances for the Lions since signing for them in the summer of 2008.
He progressed through the ranks at Galway United and later featured for Barry Town and West Ham before returning to his first club.
Derry was Forde's next stop and he won three cup competitions with the Candystripes, then moved back to the English leagues with Cardiff and Millwall.
He helped the Londoners win promotion to the Championship via the play-offs in 2010 and was named the club's Player of the Year in 2013/14.
Forde has won 24 Republic of Ireland caps and was part of the squad that travelled to Poland for Euro 2012.