The decision, announced by IRB Chairman Bernard Lapasset at the Burlington Hotel in Dublin, was approved by a vote of 16 to 10 and ratified Rugby World Cup Limited's recommendation announced last month.
"All the tenders were of a very high standard and each Union demonstrated that they could host an excellent Rugby World Cup. It is a tribute to the health of the Game and the enormous prestige of RWC that the competing bids were so strong," said Lapasset.
"Both Italy and South Africa submitted extensive and compelling tenders. I would like to thank them on behalf of the IRB Council for the quality of their work and their dedication to the process.
"The Tender Analysis Report and the RWCL Board's recommendation were carefully studied by the Council and their assessment concluded that the selection of England and Japan would provide the best combination of host Unions to drive the ongoing development of the Game worldwide.
"We believe that the succession of England and Japan as host nations for RWC will create new opportunities and help maximise commercial revenues for re-investment in the Game.
"It is an exciting combination for Rugby World Cup and one which we think will enable the sport to reach developing Rugby markets and therefore contribute to the continued growth of the Game and its values worldwide.
"The commercial success of RWC is an important element in the progression of our Game and means that developing Rugby markets be considered for the tournament to both reflect and assist the Game's strategic vision and evolution.
"We are confident that England will deliver a spectacular tournament in 2015 and that Japan, as the first Rugby World Cup host nation in Asia, will mark the beginning of a very exciting chapter in the history of this great tournament
The announcement of the RWC 2015 and RWC 2019 Host Unions is the culmination of an extensive tender process that kicked off in August 2008. It is also the first time that two tournaments have been awarded at the same time.
As the world's third-largest sporting event, Rugby World Cup is the driving force behind the global development of Rugby worldwide. The tournament's commercial success provides the IRB with the platform to invest up to £150 million between 2009-2012 across all 116 Member Unions in the form of annual Union grants and the Strategic Investment Programme that is designed to increase the competitiveness of the Game.