The Tokyo Olympics will take place between 23 July and 8 August next year after the Games were postponed for a year due to the coronavirus pandemic.
The International Olympic Committee confirmed the news on Monday, which followed a meeting of the Tokyo 2020 organising committee.
A decision to postpone the Olympic and Paralympic Games was taken last week by the IOC and the Japanese government because of the accelerating threat posed by the pandemic.
A statement from the IOC also confirmed the new dates for the Paralympic Games, which will now take place from 24 August to 5 September.
"These new dates give the health authorities and all involved in the organisation of the Games the maximum time to deal with the constantly changing landscape and the disruption caused by the Covid-19 pandemic," the statement read.
"The new dates, exactly one year after those originally planned for 2020 also have the added benefit that any disruption that the postponement will cause to the international sports calendar can be kept to a minimum, in the interests of the athletes and the international federations.
"Additionally, they will provide sufficient time to finish the qualification process. The same heat mitigation measures as planned for 2020 will be implemented."
The confirmation of the new dates comes less than a week after the forced postponement of the Games.
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."
Tokyo 2020 organising committee president Yoshiro Mori said he had proposed the time frame to the IOC, and that Bach had agreed following consultations with the international sports federations.
"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," Mori said.
"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."
International Paralympic Committee president Andrew Parsons added: "When the Paralympic Games do take place in Tokyo next year, they will be an extra-special display of humanity uniting as one, a global celebration of human resilience and a sensational showcase of sport.
"With the Tokyo 2020 Paralympic Games 512 days away, the priority for all those involved in the Paralympic movement must be to focus on staying safe with their friends and family during this unprecedented and difficult time."
Athletics' global governing body has said it will seek new dates in 2022 for its World Championships, which had been scheduled for next summer.
"We are now working with the organisers of the world athletics championships in Oregon on new dates in 2022 for our world athletics championships," World Athletics said in a statement.
The championships had been scheduled for 6-15 August in Eugene, Oregon.
Team Ireland chef de mission Tricia Heberle welcomed the clarification of a date, and said: "Now the athletes have a start date for the Games, they can work with their performance directors and coaches to start mapping out preparations.
"Importantly for athletes and sport, the next information we need clarity on are any changes to qualification and the rescheduling of qualification events. This will take some time, so in the short term the focus remains the same - stay healthy and safe over the coming months.
"The priority now is for everyone to following the government guidelines to protect Ireland and the rest of the world against further spread of this virus.
"A July 2021 start means that we have plenty of time to reactivate preparatory plans and for athletes currently in modified training or on a break of sorts, this period of time can still allow some positive impact on performance.
"If we are smart, this enforced break can make Team Ireland even better."
Paralympic Ireland chief executive Miriam Malone echoed those sentiments.
"Paralympics Ireland welcomes the announcement of a new date of 24 August for the 2020 Paralympic Games.
"This gives more certainty to our athletes, their support teams and our own high performance team, who can now plan their preparations for the competition."