The Senegalese international is keen to play regular first-team football as he bids to earn a place in his country's squad for this summer's World Cup.
But he's made only four appearances in all competitions for Newcastle this term and has headed to the Yeni Sivas 4 Eylül Stadyumu for the remainder of the season.
Saivet joined Newcastle from Bordeaux two years ago but spent last season on loan with Saint-Etienne. He scored against West Ham earlier this season in December and has made a total of eight appearances for the Magpies.
Sivasspor are currently eighth in the Turkish Süper Lig.