The former Nottingham Forest midfielder, who was most recently with Barnet, has become boss Justin Edinburgh's fourth summer signing after impressing during pre-season.
And Edinburgh is well acquainted with Byrne having been his manager for a season at Rushden and Diamonds.
"I don't think he needs time to impress because I know what he's about but i gives us time to move things about," he said.
"If we're successful on the pitch the budget will increase and will be able to increase the length of Mark's stay. We're delighted to get the deal done."
Byrne added: "I'm delighted to have signed. It's been ongoing for the last couple of weeks so I'm pleased it's all done now."