The 21-year-old's deal with Monchengladbach still has 18 months left to run, but he has turned down the offer of an extension.
He has emerged as the leading contender to replace Victor Valdes at Barcelona in the summer amid speculation the Spanish champions will pay in the region of €12million (£10million) to sign ter Stegen.
The keeper confirmed his decision to reject a deal with Gladbach and now wants to focus on the second half of the Bundesliga season.
"I have thought about it for a long time and told Max Eberl and the club today that I do not want to renew my contract at the present time," ter Stegen told the club's official website.
"I think everyone knows that I'm Borussia through and through, so it was a hard decision for me. I hope the fans will understand and accept it.
"I owe the club an incredible amount. We want to play together as a team for a good second half of the season now."
Monchegladbach's sporting director Max Eberl said: "Marc is a top boy who has superior skills.
"He will still be playing for Borussia for the next six months and will contribute with his performances so that we can succeed.
"The fact that it took so long to make a decision shows that he has been working very closely with our contract offer."