The 23-year-old has signed a five-year contract with the Bundeslgia side.
Kacar told HSV’s official website: “I am very happy that it worked out effectively. The last few days were a bit hectic, so I am happy now to go to team’s training camp.
“HSV is a great club that has a great history and want to achieve great things. I think I can develop myself at HSV optimally and contribute with my strengths.
“It is the ideal club for me. That’s why I’m here and I want to stay here for a long time.”
Hamburg’s sporting director Bastian Reinhardt said: “Gojko is a great player with great potential and good character. We are pleased that the change has worked. With him we have another player in the squad who is very flexible.”
