The 25-year-old scored 27 times last season - and had many clubs understandably chasing his signature after he turned down a new deal.
Solihull managed to convince him to come and fills the boots left by departing striker Adi Yusuff.
McCallum said: “I’m very excited to be joining a club with such big ambitions – it looks to be heading in a great direction.
“I was very impressed with the plans and believe that we can achieve big things. The key thing that made me sign was the ambition and desire for the club to get to the next level.
“My aim personally is to score more goals than I did last year and, in doing so, hopefully help the team achieve the main goal of getting promoted!”
Manager Tim Flowers added: “I am absolutely delighted to welcome Paul to Solihull Moors. He is a player we have admired from afar for some time and to have secured his signature is a major coup for us.
“His presence, goal scoring and technical skills will be a huge asset for us as we look to build on last season. He joins a strong squad of players and I look forward to working with him."