Copenhagen was awarded the event by a vote taken by organisers InterPride.
The result of that vote was announced by Happy Copenhagen, the Danish organisation responsible for the bid to bring the event to the Scandinavian country.
The organisers expect up to 500,000 people from around the world to visit the city during the event.
Happy Copenhagen lead secretary Lars Christian Østergaard told news agency Ritzau he was delighted at the decision.
“Right no we're all celebrating and are happy. We did it,” Østergaard said.
“We have ambitions to spread across the world and to set the agenda within the LGBT community. We believe that Copenhagen can do that,” he continued.
The organisation hopes that 2021 will be a double event year for the city, with a decision on a host for the LGBTQ sporting event EuroGames to be made in March 2018.
WorldPride is a ten-day event.
“There will be a good mix of cultural events and concerts. The will be a huge human rights conference,” Østergaard said.
“There will also be a separate sports event. There will be rainbow flags all over the city and the whole city will be invited,” he added.
The bid to bring the event to Copenhagen was launched in 2015. The budget for planning and executing the event from 2018-2021is 94 million kroner (13 million euros), financed by contributions by the Hovedstad (Capital) regional administration and several local municipalities, including in the Swedish city of Malmö.
READ ALSO: Denmark to host Darts World Cup in 2021
Editor's note: a previous version of this article stated erroneously that the cost of the bidding phase, rather than the planning and execution of WorldPride 2021 in Copenhagen, was 94 million kroner. This has now been corrected.