The club say they have fended off interest from higher up the football pyramid to secure the services of the Irish defender.
Byrne, 26, has previously played for League of Ireland club Cabinteely in his native Dublin, along with Frickley Athletic and Boston United.
On his capture, manager Andy Coyles said: “Karl is a fantastic signing for us. He is an exciting signing who I think will really push the team on to another level, both in his ability on the pitch and also his charisma and enthusiasm around the changing room and the club.
“We’ve had to be exceptionally patient due to the level and the amount of interest that clubs have shown in Karl – clubs from the Northern League right up to the National League North.
“He’s bought into the project and the ambitions that the football club have, and this is the first signing that I’ve been involved in where there’s been so many different parties who have contributed to getting it over the line.”
Byrne becomes the club’s 10th summer signing, following in the footsteps of Zak Atkinson, Declan Bisset, Callum Elliott, Adam Mitchell, Cyril Giraud, Kieren Aplin, Mark Foden, Mark McLeod and the returning Danny Craggs.
Photo Credit: Consett AFC