Both deals were to expire on Wednesday.
Captain Chiellini will turn 36 in August and said he intends to play on for at least one more year.
He has been in the Juve squad since 2005, amassing 509 competitive appearances for the club, scoring 36 goals.
As for Buffon, the goalkeeper has 669 games under his belt in the Bianconeri jersey since arriving from Parma in 2001.
Need a VPN? Or seeking to switch? Then support Tribal Football by clicking here to sign up with our official partners NordVPN. Not only will you receive the best VPN experience, but also great discounts by signing up via Tribal Football. Thanks for your support!