Clubs in Serie A will be name as many as 12 substitutes, with the measure taking effect immediately, after lobbying from a number of key figures.
The Italian Football Federation (FIGC) announced the rule change on Tuesday night following a formal request from the Serie A president Maurizio Beretta.
It means clubs competing in Serie A, Coppa Italia, Italian Super Coppa or Primavera league matches will be permitted the extra reserves.
One of the strongest advocates of the move was the Napoli president Aurelio De Laurentiis, who spoke to Sky Italia shortly after the announcement.
"I thank the international and national organisations that have introduced this rule of absolute common sense," he said.
"I made the proposal while ago because I thought it was important to give more choice to the coaches for changes during games, but also because it was unfair to send called up players to the stands as it threatened to see their value plummet. It proves it is not impossible to change the world of football, but we have stood still for too long."
His thoughts were echoed by the Palermo president Mauricio Zamparini, who said his club "have two players for every role, so we can only benefit from this new development".
However, Roma coach Zdenek Zeman told Corriere dello Sport: "It doesn't change much for me, as in my experience a total squad of 18 is sufficient."