The 25-year-old centre-back moved to the Bay Arena ahead of the 2012-13 season and made 31 Bundesliga appearances in his debut campaign.
However, he fell down the pecking order at Leverkusen and spent the first half of the present campaign on loan at Mainz.
Manager Mark Hughes has now swooped to bring the Germany international to the Britannia Stadium, initially on a temporary basis.
"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," Hughes told Stoke's official website.
"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 could make his debut in Sunday's Premier League encounter at Arsenal.
