The promising youngster has decided to leave his boyhood club in search of regular first-team football with Thorsten Fink's side
HSV were keen to add some more depth to their defence and they see the 22-year-old Sobiech as a valuable addition to their squad.
The centre-back has signed a contract until the summer of 2016 with Thorsten Fink's outfit, and he admitted HSV's determination to seal the move helped sway his decision.
"I had already agreed terms with HSV a while ago and was determined to move here. The fact that really wanted me was vital in my decision to join, Sobiech told the official Hamburg website.
"I want to get as much playing time as possible. The most important thing now is to integrate into the team."
Sobiech is a product of the Dortmund youth academy, but he failed to break into the first team with the Champions League finalists.
He spent last season on loan at Greuther Furth after previously wearing the St. Pauli jersey on a temporary basis.