The 27-year-old striker becomes the seventh signing of the summer as Hamburg continue preparations for the new campaign.
Moffi has been handed the prestigious No. 9 shirt and will be expected to lead the club’s attacking line.
The move gives the forward an opportunity to relaunch his career in Germany and establish himself as a key figure for Die Rothosen.
“The coach was really convincing in our discussions. The location, with its fantastic fans, and the club’s overall direction also played a role in my decision,” Moffi told the club’s official website.
“Even though HSV played in the second division for a few years, the club is still a big name, all over the world.
“When I told my father about the interest, he immediately knew which club I meant and was thrilled. For me, it was positively crazy. I’m all the happier now to be a part of the club’s history.”