Last week, the Olympics – which were due to start on July 24 – were postponed due to the global spread of coronavirus.
A joint statement from the IOC and Tokyo 2020 organising committee later clarified the Games would be moved "to a date beyond 2020 but not later than summer 2021".
The IOC has now ratified the new dates, while announcing the Paralympics will take place from August 24 to September 5.
In a conference call on Monday, IOC president Thomas Bach said: "I want to thank the International Federations for their unanimous support and the Continental Associations of National Olympic Committees for the great partnership and their support in the consultation process over the last few days.
"I would also like to thank the IOC Athletes' Commission, with whom we have been in constant contact. With this announcement, I am confident that, working together with the Tokyo 2020 Organising Committee, the Tokyo Metropolitan Government, the Japanese Government and all our stakeholders, we can master this unprecedented challenge.
"Humankind currently finds itself in a dark tunnel. These Olympic Games Tokyo 2020 can be a light at the end of this tunnel."
An IOC statement said the decision was based on three main considerations; to protect the health of athletes and support the containment of COVID-19, to safeguard the interests of athletes and of Olympic sport, and the global international sports calendar.
It added the new dates provide health authorities ample time to deal with an ever-changing landscape, while sufficient time will be given to finish qualification processes where necessary.
The IOC said heat mitigation factors as planned for 2020 will also still be implemented.
— Olympics (@Olympics) March 30, 2020
The President of the Tokyo 2020 Organising Committee, Mori Yoshiro, said: "I proposed that the Games should be hosted between July and August 2021, and I really appreciate that President Bach, having discussed this proposal with the various international sports federations and other related organisations, kindly accepted my proposal.
"A certain amount of time is required for the selection and qualification of athletes and for their training and preparation, and the consensus was that staging the rescheduled Games during the summer vacation in Japan would be preferable.
"In terms of transport, arranging volunteers and the provision of tickets for those in Japan and overseas, as well as allowing for the COVID-19 situation, we think that it would be better to reschedule the Games to one year later than planned, in the summer of 2021.
"Notwithstanding the postponement of the Olympic and Paralympic Games for the first time in history, and various other issues that have already been highlighted, the event schedule is the cornerstone of future preparations, and I am convinced that taking this decision promptly will help speed up future preparations."
The rescheduling marks the culmination of a frantic period.
A little over two weeks ago, Japan prime minister Shinzo Abe and the IOC both insisted there was no need to postpone the Games.
However, the worsening situation of the global spread of COVID-19 soon made such proclamations look extremely premature.
There have been 737,567 confirmed cases of coronavirus globally, with 34,998 people having died - as per World Health Organisation figures on Monday.