The 20-year-old, who was also linked with Arsenal, was part of the Germany squad who stormed to World Cup triumph in Brazil, but failed to get a game during the tournament.
Bundesliga runners-up Dortmund have revealed that Ginter has put pen to paper on a five-year deal.
"A boyhood dream came true for me today," The AP quotes Ginter as saying. "I have always been a big Dortmund fan and now I can wear the shirt of my favorite club. I want to take the next step in my sporting development in Dortmund."
The defender made 70 Bundesliga appearances for Freiburg.