Cooper had been released by Crawley Town at the end of the season, but after spending a loan spell at Fratton Park during the last campaign, the former Bournemouth man has admitted that he is excited upon his return.
The 29-year-old told the club's official website: "It's nice to be back concentrating on football after an extended summer. I'm pleased to get the deal done and to come back to a club that now has a different feel about the place.
"Everybody knows about the problems last season with so many players coming and going, but it's nice to come back for a new beginning.
"The pitch and the stadium look great and I'm looking forward to getting going once again."
Cooper scored twice in 14 appearances for Portsmouth last season.