The 36-year-old forward, who joined the Turin club as an 18-year-old in 1993, is Juve's all-time record goal-scorer and most-capped player with 205 goals in 495 Serie A appearances.
"The one link between Juve's different homes has been our captain Alessandro Del Piero," Agnelli said at a club shareholders' meeting on Tuesday. "He wanted to stay with us for one more year which will be his last in black-and-white."
Del Piero had offered to play for nothing this season, the inaugural year of the club's 40,000-capacity privately-owned Juventus Arena, before signing a one-year contract in May.
"The new stadium is testimony to Exor's [the Agnelli family's holding company] ability to invest in years of crisis," said Agnelli, who announced record club losses of 95.4 million euros for the 2010/11 season.
"The balance for the year is intolerable - the worst in the club's history, but necessary to keep Juventus competitive.
"The new stadium represents a break with the past. We are the first club in Italy to undertake such a project and keep up with our European competitors."
Del Piero, who has won five scudettos and the 1996 Champions League title with Juve as well as a World Cup winners medal with Italy, has played only a bit part this season as Juventus, under new coach Antonio Conte, have climbed to the top of Serie A.
"The squad has been rebuilt completely and we've put the emphasis on youth," said Agnelli. "The team needs to grow but we are now competitive and can look forward to matching results that form part of this club's history."
Italy's best supported club, Juventus have won a record 27 Serie A titles but none since being stripped of the 2005 and 2006 scudettos because of their involvement in the Calciopoli scandal.
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