The 36-year-old Iceland defender recovered from serious injury to make 29 appearances for Pompey last season and earn a new deal.
"We are really pleased about Hermann deciding to return. He is a good lad who showed some real character coming back last year," Pompey boss Steve Cotterill told The News.
"He has got another year's deal so, hopefully, he will come back after a bit of a break refreshed and raring to go again.
"We've given him a bit of a longer break like a couple of the others because they were still playing over the summer.
"It is now only a matter of him coming back into the UK and signing the contract. I expect that will all be sorted out in the next 48 hours."