The 25-year-old beat Patricia Mayr-Achleitner in the quarter-finals in Austria on Friday to join Serena Williams, Victoria Azarenka, Agnieszka Radwanska, Li Na, Petra Kvitova, Sara Errani and Jelena Jankovic in the field.
Kerber, who featured in the WTA Championships for the first time last year, ensured the October 22-27 event would have eight players from different countries for the first time.
"I am so excited to be returning to Istanbul for the WTA Championships," the world number 10 said in a media release. "The fans last year were amazing and I look forward for the chance to play against the best players in the world."
World number three Maria Sharapova will miss the championships because of a shoulder injury.