The teenager will be loaned back to the National League outfit for the remainder of the season. Maxwell has made 32 appearances for the Harries since breaking their youth system in December 2014.
Chief Executive, Colin Gordon told the club website:” Everyone at the club would like to congratulate Luke on his signing with Birmingham City.
“The transfer benefits the club financially, but it was crucial for us that we were able to keep Luke with us until the end of the season. He’s a big part of our squad and will play a large role in our battle between now and the end of the campaign.”
Gordan said:” Luke has earned a lot of admirers and I know this is a move he’s delighted to be making – Birmingham have been a pleasure to deal with and they know they are getting a player who has the potential to really succeed in the game.
“We’ve stressed that, as a club, our future has to be creating and producing our own talent and giving them a platform to succeed. But as we’ve proved with this deal, we aren’t just concerned with cutting our losses and making a quick sale.”