Chairman Eddie Mitchell has, in the past few minutes, confirmed that the Football League have rubber-stamped the former Weymouth stopper's move to Dean Court.
The 6ft 4in Stewart, who trained with his new team-mates at Canford School this morning, will provide competition for number one Shwan Jalal, with the club's other stopper Dan Thomas currently sidelined through a knee injury.
Boss Howe told the Echo: "Jon's been around for a while. He was at Weymouth under Jase and he's been at Portsmouth for a couple of years and we've kept tabs on him during his time there.
"He's got all the attributes to be a top goalkeeper."
Chairman Mitchell added: "It's great to be able to accomodate more players for Eddie."
MORE ON THIS STORY IN TOMORROW'S ECHO.