The Black Cats originally announced the link-up in the summer of 2015, and the extension to the current agreement sees Dafabet become one of the club’s longest-serving main sponsors.
As part of their ongoing commitment, Dafabet will be undertaking a number of fan engagement initiatives, beginning with the gift of a giant crowd-surfer flag to fans group Ha’way the Flags, to be used at the Stadium of Light on matchdays.
The new flag will feature a current Sunderland first-team player, and fans will be asked to vote online for the player they would most like to feature in the design.
Sunderland commercial director, Gary Hutchinson, said: "Dafabet have a great understanding of football and the football industry and over the last year we have seen our partnership with them flourish on a global level.
"There is a real synergy between the club's aims and objectives and what Dafabet want to achieve.
"They are a major player in the football and sport sectors and we are delighted to align ourselves with them in the longer term, giving us increased opportunities to grow and develop our relationship in the coming years."