The tournament, which features the season's top eight singles players, is moving to Istanbul from Doha this year and, as a result of the action currently taking place at the US Open, Wozniacki and Sharapova have now booked their trips to Turkey.
Wozniacki has played in the season finale in each of the last two years, finishing tunner-up to Kim Clijsters in 2010, while Sharapova is returning to the prestigious event for the first time since 2007. She won the title back in 2004.
World number one Wozniacki, who has won six WTA titles so far this season, said: "I'm so excited to qualify for the Championships in Istanbul. It's always a big goal for the top players to end the year there.
"It's a wonderful city and it will be great to play in front of a new set of fans. Hopefully we can put on a good show and provide an exciting end to the year."
Sharapova added: "I am so happy to have booked my spot in Istanbul. I haven't been to the year-end Championships since 2007 and I've really missed competing in one of the most exciting and important events of the year."
French Open champion Li Na, Wimbledon winner Petra Kvitova, Victoria Azarenka, Vera Zvonareva, Marion Bartoli and Francesca Schiavone currently hold the other six qualifying positions.
The tournament takes place from October 25-30.
The news comes soon after Andy Murray and Roger Federer were confirmed as qualifiers for the equivalent men's event - the ATP World Tour Finals in London.
As a result of their US Open progress, Murray and Federer join Novak Djokovic and Rafael Nadal in the eight-man field at the O2 Arena.