The Frenchman has signed a four-year contract at Hillsborough, and Owls boss Dave Jones has revealed that the club have worked hard to put a deal together for the 21-year-old.
The 56-year-old told the club's official website: "We have done a lot of hard work to get him here.
"Other clubs were aware of what he did here last season and wanted him on board, but he really enjoyed his time here and wanted to come back.
"To get Jeremy on a permanent transfer represents a really good signing for the football club, and it is a statement of intent because he is a really talented footballer. He is young and has a terrific future in the game."
Helan made 28 appearances during two loan spells at Wednesday last season.