Harrington replaces Open champion Ernie Els, who has pulled out with a left ankle injury, and in an event meant to bring together the season's four major winners is up against Masters champion Bubba Watson, US Open winner Webb Simpson and last year's USPGA champion Keegan Bradley - himself a replacement for Rory McIlroy.
Northern Ireland's world number one qualified with his USPGA victory in August, but is defending the BMW Masters title in Shanghai this week, while second and third alternates Graeme McDowell and Tiger Woods are also honouring commitments to play in Asia.
Harrington said: "While my entry is under unique circumstances, I am excited to compete in the event again. I came close the last two times I was there, losing in play-offs to Angel Cabrera in 2007 and Jim Furyk in 2008, so maybe the third time will be a charm."
Els, winner in 1997 and 2010, stated: "I am bitterly disappointed. It is a great reward for winning a major and something I have enjoyed in the past and was looking forward to again.
"Unfortunately I sprained my left ankle a few days ago and while it isn't too serious and should recover relatively quickly, I have been advised not to try and play on it."
The winner receives £375,000 and the runner-up £187,500.