The shock signing of the 38-year-old comes as the Blues prepare to deal with the impending departure of Thibaut Courtois for Real Madrid, and while the hunt remains on for a high-calibre replacement, Green has been drafted in to provide experience and options in the goalkeeping department.
Green arrives at Stamford Bridge on a free transfer, having been released by Huddersfield Town over the summer, and has previous top-flight experience with West Ham United, Norwich City and Queens Park Rangers.
"It has been a whirlwind 24 hours," Green told the Chelsea website. "You are thinking about your career and where you want to go and then you get a phone call like this, and it is a short conversation.
"It has been a pretty dramatic time for me and I can't wait to get started. I am absolutely delighted and it is a thrill and an honour to be here."
Courtois, meanwhile, is said to have agreed personal terms with Madrid in the last 48 hours, leaving the two clubs still negotiating over the transfer fee.