The young midfielder looks destined for a future with BVB after penning an extension, but he will play out the next two seasons with Bruno Labbadia's men as part of the agreement
The midfielder, 20, is regarded as one of BVB's most promising youngsters but has so far struggled to break into coach Jurgen Klopp's plans, with midfielders Ilkay Gundogan and Sven Bender currently standing in his way.
As a result, he will now continue his development at the Mercedes-Benz Arena until 2015 before returning to Dortmund in the hope that he can forge a career with the Champions League runners-up.
Stuttgart sporting director Fredi Bobic said of the move: "He fits in perfectly with what we want from a player. He is young, technically gifted and has a very good understanding of the game.
"And last but not least, he can be used in several positions. He has all the skills to play a key role in our team."
Leitner, who arrived at Dortmund in the summer of 2011 from 1860 Munich, was equally as enthusiastic about the move.
"Stuttgart are simply a great club with great traditions. I think we can achieve a lot here. I have a great desire to help Stuttgart return to where they belong," he added to reporters.
Despite his struggles to claim regular game time, Leitner has featured 42 times for the Schwarzgelben in the Bundesliga.