The world number five will be playing in the season-ending event for the fourth time and joins Novak Djokovic, Roger Federer, Rafael Nadal and Andy Murray as the players already confirmed.
"I am very happy because to qualify for the Barclays ATP World Tour Finals is a great achievement," Ferrer told the ATP Tour's official website.
"It's always one of my goals at the beginning of each year. I look forward to coming back to The O2 in London to play against the best players in the world in November.
"The atmosphere in the stadium is incredible there."
Wimbledon doubles champions Jonathan Marray and Frederik Nielsen have also booked their spot at The O2.
"To be able to cap off the season by competing against the world's best doubles teams in front of a home crowd at The O2 in November will be incredible," said Marray.
"We had a great run at Wimbledon this summer, so hopefully we can reproduce some of that form in London this November."
The Bryans, Max Mirnyi and Daniel Nestor, Robert Lindstedt and Horia Tecau, and Leander Paes and Radek Stepanek are the other teams in the doubles event.