The midfielder has signed a three-year deal at the WIRSOL Rhein-Neckar Arena, joining for a fee believed to be under the €2m mark.
After struggling to get game time in the Hanseatic city and two loans, he will be hoping to nail down a spot in the Hoffenheim side.
Demirbay spent his early years swapping between various Ruhr clubs, including FC Schalke 04, SG Wattenscheid 09 and Borussia Dortmund.
After leaving BVB - for the first time - he made a big impression in the Wattenscheid youth teams and was brought back to Signal Iduna Park.
The now 23-year-old returned for two seasons and continued his form, but ultimately needed first-team football to further his career.
Bundesliga chances few and far between
Hamburg were the side who seemed prepared to give him that chance. Yet he was to be given just 55 minutes of Bundesliga action in that first campaign in the North.
Desperate to get on the pitch, Demirbay headed for 1. FC Kaiserslautern on a one-year loan deal.
He impressed during his time at the Betzenburg, seemingly earning a shot at the HSV first-team as he helped them to almost make a Bundesliga return.
That was not the case, and he was then loaned to Fortuna Düsseldorf; 11 goals and five assists in 26 games showed what Demirbay could do.
Finally, Hoffenheim were the side to see his potential. After getting him for a bargain price, they can expected a more than reasonable return.
Rosen raves about Demirbay
Alexander Rosen, the club's sporting director, spoke highly of Demirbay's ability: “Kerem was one of the outstanding players in the 2. Bundesliga last season."
Rose, talking to the club website, feels his new signing “is an athletic and creative attacker who shows great determination in front of the opponents’ goal”.
Demirbay himself added, “The intensity with which TSG looked to get me to sign showed was a great compliment and It’s necessary for me to repay their faith."
He concluded, "I want to prove myself in the Bundesliga and I have the optimum conditions to do that here.”