Barker told the club's official website: "I'm very pleased. Once we sat down and had the discussion, it didn't take very long to be honest. I enjoyed my initial six weeks, which I thought I would anyway, but I did even more than I thought I would.
"We've almost run out of football on TV now and I always know you are ready to come back to work when you're bored, I got bored about 10 days ago! I'm ready to start again now."
Executive director Andrew Cullen added: "He is a very talented coach who has experience of both playing and managing at this level and we're excited to see him continue his work with the first-team and the younger players to help drive the football club forward."
Barker had a three-month spell in charge of Portsmouth earlier this year, but left before the end of the season.