The 34-year-old Australian, who has partnered Atkinson since he joined the team in 2004, has decided to return home in order to devote more time to his personal and business commitments.
"Competing in the World Rally Championship is far more than just a job, and while I really have enjoyed my time with the team I’ve simply come to the point now where I want to do other things,” said Macneall.
"Having made up my mind to go, it wouldn’t be fair on Chris for me to carry on with anything less than 100 per cent commitment, and for this reason I felt it would be best to step down straight away.
"I’ll continue to follow the sport very closely and I wish Chris, Petter and the whole Subaru team the best of luck in the future."
Atkinson has been partnered by Macneall on all of his 36 WRC starts with Subaru.
"I’d like to thank Glenn for all his hard work since our first rally together in Australia 2004,” Atkinson said.
“I’m sorry that he has decided to go, but I can understand his reasons and in the long term I’m sure a clean break now is the best way forward.”
Subaru World Rally Team managing director Richard Taylor said: “Glenn has been part of Subaru’s rallying programmes ever since he joined our team with Toshi Arai in 2001.
"He is an experienced and respected competitor in both the Australian and World Rally Championships. On behalf of Subaru, Chris and the rest of our team I’d like to thank him for his contribution over the years and wish him the best of luck in the future.”
An announcement concerning Chris’s new co-driver will be made before next month’s Rally Argentina.