Hughes was still contracted to the Saddlers but the Fury fought hard to get him a release and Middleby was delighted when they finally signed the former Everton man.
"It's a massive coup for us, huge," Middleby told the Townsville Bulletin.
"He's a leader, he's been a captain at Walsall, he's been through the Everton junior ranks and he's a leader and for that centre-back position it is really what we were looking for. It's a great signing.
"Technically he's very good, he's good on the ball and, from what I've heard, very big and strong.
"He's been playing a very good standard in England, very good, (and) he's got a lot of experience for that young age, so I think it's great for the team, great for the club and great for everyone."
Hughes, who will arrive in Townsville tomorrow, told Walsall's official website that the move was simply a great opportunity.
"It is a once-in-a-lifetime opportunity and if I don't go for it I think I'll always be thinking 'what if?'," he said.
"These opportunities don't come round very often and, after much deliberation, I want to give it a go."