The American will now bid to defend her title in Istanbul from October 22-27.
The prestigious tournament features the season's top eight players and French Open champion Williams is already guaranteed to be among them.
That is thanks to a superb 51-3 win-loss record in 2013, one which has landed her seven titles in total and includes a career-best winning streak of 34 matches.
"I'm very excited to have qualified for the TEB BNP Paribas WTA Championships and have the opportunity to return to Istanbul in October to defend my title," said Williams.
"The support we received from the fans at last year's championships was overwhelming and it's going to be a very special feeling returning to Turkey and playing in that incredible atmosphere once again."
WTA chairman Stacey Allaster said: "I congratulate Serena on becoming the first player to secure her place at the TEB BNP Paribas WTA Championships-Istanbul.
"Serena is having yet another extraordinary season on tour, and continues to be one of the sport's greatest champions. She has earned the opportunity to defend her title and be part of our very special season finale in Istanbul."
Istanbul is staging the tournament for the third and final time this season before it moves to Singapore in 2014.