It is understood the club rejected the cash lure of a pay day loan company in favour of a relationship more in keeping with it's supporters.
It was good news for Chairman, Norman Smurthwaite, who recently took full control of the club, and he was delighted by a deal which he believes has massive benefits for both parties.
"I looked at a number of potential sponsors for a club in this demographic, but this one just couldn't fit better," he said. "It is just what I wanted for the club. I think there will be great synergy between us and we'll certainly both benefit.
"The GMB is a renowned national union which has great representation in this area and I think we can go forward together.
"They are an organisation that fight for people's rights, and many of those people come to watch Port Vale on a Saturday afternoon.
"This is a community club and this kind of partnership is what we are all about.
"It's not based purely on financial reasons because there were companies who wanted to spend more with us, but I felt they didn't sit right for the area or the fans.
"The GMB are an excellent brand who are good for their members and I'm sure we can be a success together."
Smurthwaite said it was difficult to put a figure on the value of the deal.
"Obviously there is the initial amount," he said, "but then there's the extra business it will bring to the club."
The union has sponsored Vale's first-day opponents Brentford in the past, but it is their previous connection with Fulham during boss Micky Adams's time at Craven Cottage which prompted this deal.
"This was down to Micky initially," added Smurthwaite. "They sponsored Fulham when he was there and kept a strong friendship with him. Now they have come to us.
"They're going to encourage their membership to become fans of Port Vale, either physically or from a distance. In turn, we'll try to form relationships with local employers who have GMB members."
GMB General Secretary Paul Kenny added: "Port Vale is a community club, our members live locally, so we think we can bring something to the club.
"We don't want to be absent sponsors, we want to be engaged with all levels of the club and support the area."