The 24-year-old midfielder has put pen to paper on a four-and-a-half-year deal and is Sunderland's fifth signing during the current transfer window.
"Wahbi is a quick, dynamic attacking player," manager Sam Allardyce told the club's official website.
"He has many attributes, not least his delivery from wide areas and set pieces and of course his ability to score goals.
"His versatility will certainly complement our existing forward options and I'm delighted to welcome him to the club."
Khazri started out at Bastia and in 2014 moved on to French rivals Bordeaux, for whom he made over 50 appearances.
He has scored six goals in 13 appearances for Tunisia since making his debut in 2013 and has featured in both the African Nations Cup and World Cup qualifiers
Khazri could make his debut in Tuesday night's home league game against Manchester City and joins goalkeeper Steve Harper, defenders Lamine Kone and Jan Kirchhoff and striker Dame N'Doye as new Sunderland signings.
Source : PA