The 25-year-old central defender, who has been capped twice by his country, plays for Bayer Leverkusen but spent the first half of this season on loan with Mainz.
Wollscheid, who has also played for Nuremburg and has made more than 50 Bundesliga appearances for Leverkusen, completed the formalities of his loan switch earlier today before training with his new team-mates for the first time.
Chief Executive Tony Scholes said: "Philipp has an impressive pedigree in the game. He is keen to make an impact in the Premier League and we're delighted he has chosen to join Stoke City.
"He's joining us on loan, which gives him an opportunity to get to know the Club and us an opportunity to get to know Philipp."
Manager Hughes added: "Philipp is a player we've been aware of and have been tracking for some time and he will add to the competition for places in the centre of our defence.
"He's got presence, technically he is good, he has played at a high level and he has gone for big money in the past and to get a German international at relatively young age is a good deal for the Club.
"He's genuinely excited about the prospect of playing in the Premier League and is confident of making a big impression as a Stoke player."
Wollscheid has been allocated squad number 26.