Organisers had been confident of sealing the contract worth 68 million euros .
Organisers had been confident of sealing the contract worth 68 million euros ($72 mn) after successful negotiations with Formula One's commercial supremo Bernie Ecclestone in September.
"Signed! Formula One boss Bernie Ecclestone and ACI President Angelo Sticchi Damiani yesterday signed the agreement to keep the Italian Grand Prix on the F1 calendar for the next three years," the ACI said in a statement.
"We've managed to avoid the terrible hypothesis of seeing Italy lose after 70 years one of the most prestigious, historic and exciting car races in the world," the ACI president added.
The Italian Grand Prix was first held at Monza in 1921 and is the oldest race on the calendar. It was one of the inaugural F1 world championship races in 1950.
The 2016 world champion Nico Rosberg won this year's edition of the Italian Grand Prix.
The contract extension had been the subject of prolonged talks over the past year, notably concerning the cost of the event.