The 42-year-old has been with the Turin club since 2001, save a one-year spell at Paris Saint-Germain in 2018-19, after which he returned to the Allianz Stadium.
And he and veteran defender Giorgio Chiellini, the club captain, have both signed contract extensions that will keep them at Juve until June 2021.
"There are players who need no introduction," a club statement reads.
"Champions whose story speaks for itself, and whose connection with the shirt they wear is indissoluble.
"Examples on the pitch and in the locker room, leaders, driving forces, bearers of the Bianconeri DNA, who wear it as a second skin.
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"Gianluigi Buffon. Giorgio Chiellini. Captains, legends."
Chiellini is similarly long-serving, having move to Juventus in 2005. Buffon and Chiellini sit second and fifth respectively in the club's all-time appearance lists.