The centre-half arrives from Hannover 96 and will fill the defensive gap left by the departure of Serdar Tasci to FC Spartak Moskva.
Stuttgart are the third Bundesliga club for the 29-year-old. He previously spent three seasons at Bayer 04 Leverkusen before his switch to Hannover in 2009. He has lived and played in Germany since 2004, and conveyed to the club website his excitement at experiencing the "famed atmosphere" in the Mercedes-Benz Arena.
Haggui expressed his "delight at becoming a Stuttgart player", and went on to add that "VfB are one of the biggest clubs in Germany. I'm here to help us achieve our season aims".
He follows in the footsteps of Mohammed Abdellaoue and Konstantin Rausch, who both left the HDI Arena to join Stuttgart this summer. Haggui has made 166 appearances in the Bundesliga and scored ten goals, as well as representing his country on 80 occasions.