The midfielder, who is currently recovering from a broken leg, would have been out of contract this summer.
Pompey’s assistant manager Joe Gallen told the club’s official website: ‘We’ve missed him in the team since he broke his leg and we’re pleased that he’s on the road to recovery.
‘He’s working hard in the gym and will hopefully be out running pretty soon and available for pre-season.’
Preston are reportedly weighing up whether or not to make a fourth offer for Peterborough United left-back Andrew Hughes.
James Maddison has completed his move from Norwich City to Leicester City for an undisclosed fee.