Spreadex offers fixed odds and spread betting, as well as financial trading. The firm is regulated by both the Gambling Commission and Financial Conduct Authority.
They will become the club’s main shirt sponsors, both home and away, for the next three seasons.
The club say the deal includes ‘a commitment to work alongside the club on a range of community and charity-based initiatives.’
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Chief Operating Officer Steve Davison said: “We are all delighted to welcome Spreadex as our new Principal Partner and look forward to building our relationship with them throughout the next three years.
"It is set to be an extremely exciting campaign for the club as we return to the Championship and this partnership will also support communities within the City of Sunderland through a range of innovative initiatives.”
Spreadex CEO David MacKenzie said: “We are overjoyed to be partnering with Sunderland AFC at such an exciting time for the Club after their promotion back to the Championship. At Spreadex, we have also seen strong recent results as we continue to grow as a company and we look forward to working closely with SAFC – and their fans and community partners – during this long-term deal.
"One initiative we will be introducing immediately is a pledge to donate £100 to the Club’s designated charity for every home goal scored by the Black Cats throughout the upcoming season. We will also be looking to launch other charity initiatives in the coming months.”