Vivianne Miedema scored both goals to help the Dutch qualify for the women's showcase tournament for the first time.
The 18-year-old also scored in the 1-1 draw in the first leg of the playoff.
Miedema, who plays for Bayern Munich's women's team, put the Dutch ahead in the tie in the ninth minute before make it 2-0 just before halftime when she collected Lieke Martens' through ball and beat defender Roberta D'Adda before rounding onrushing Italy goalkeeper Laura Giuliani.
Italy, which had not qualified for the World Cup since 1999, got a goal back in the 53rd when Stephanie van der Gragt turned Sara Gama's cross into her own net.
Italy men's coach Antonio Conte and Italian football federation president Carlo Tavecchio were present.
The last finalist will be determined Tuesday when Trinidad and Tobago hosts Ecuador in Port of Spain. The two teams tied 0-0 in the opening leg in Quito.
Trinidad and Tobago finished fourth in CONCACAF qualifying while Ecuador was the third-place finisher in South America.
The draw for the FIFA Women’s World Cup 2015 is set for Dec. 6 in Ottawa.
The tournament, to be held in Moncton, Montreal, Ottawa, Winnipeg, Edmonton and Vancouver, runs June 6 to July 5.
The Women's World Cup Trophy, meanwhile, is kicking off its "Live Your Goals Tour" with a stop in Madrid this weekend.
The tour will take the trophy to all 24 participating countries, with the second stop in China on Jan. 11.
Canada (host), Australia, Brazil, Cameroon, China, Colombia, Costa Rica, England, France, Germany, Ivory Coast, Japan, Mexico, the Netherlands, New Zealand, Nigeria, Norway, South Korea, Spain, Sweden, Switzerland, Thailand, U.S.
With files from The Associated Press