The 32-year-old Iceland defender exercised a clause in his contract which allowed him to leave The Valley on a free transfer if the Addicks were relegated.
He has moved to Fratton Park two days after Pompey secured the services of former Manchester City defender Sylvain Distin on a three-year deal.
© Copyright PA Sport Ltd 2007, All Rights Reserved.
Do YOU want to write for GiveMeSport? Get started today by signing-up and submitting an article HERE: https://www.givemesport.com/writeforgms