Spieth, the 21-year-old Texan and 13th ranked player in the world will make his first trip to Australia in search of the Stonehaven Cup and line up in Sydney at The Australian Golf Club from November 27-30.
After breaking through with his first win in 2013, Spieth went toe-to-toe with Bubba Watson at the Masters this year before finishing second.
A Presidents Cup player in 2013 as a captain's pick, Spieth has this year earned his way automatically onto the USA Ryder Cup squad where he will compete in Scotland after the US PGA tour play-offs end.
He helps bolster an impressive field with defending champion and world number one McIlroy, world number two Scott and current world number seven Day already committed to play.
McIlroy famously denied Scott the Australian Triple Crown last year with a final hole birdie, kick starting his resurrection towards the top of the rankings.
"I'm extremely excited to be going to Australia as I've always wanted to go given my instructor comes from Melbourne, plus there's a lot of Australian players on tour saying how great their country is," Spieth said.