Belgium's capital city has been ruled out as a planned new stadium is still to be built and Uefa have not received the necessary guarantees.
UEFA president Aleksander Ceferin said that the four matches due to be staged in Brusselsm - three group games and one last-16 match - would be played at Wembley instead, in addition to the two semi-finals and final already scheduled to be played there.
Should the Republic of Ireland qualify for Euro 2020, they will play one of their group games in Bilbao.
"They still don't have the documents". They didn't expect a decision until January and they did not know whether that would be a yes or a no. Experts from [our] administration felt it was a high risk for UEFA to wait.
Ceferin said that the development of the Eurostadium had run into delays involving the applications for construction and environmental permits.
"We did everything we could until the last moment to make Uefa hold off, but we respect the decision", Koen De Brabander, chief executive of the Belgian Football Association, said in a statement.
As well as deciding where the first game, on June 12, will be and what to do about Brussel's difficulties, the executive committee also announced where each of the six groups' games will be played.
England's national stadium is one of 12 venues across Europe hosting Euro 2020 games.
We know what you're thinking, 'we've only qualified for the Euros three times ('88, '12, '16)' but the new 24 team format means it's now easier for Ireland to get through the group stages as we found out in Euro 2016.
Rome and Baku will host Group A, Saint Petersburg and Copenhagen Group B, Amsterdam and Bucharest Group C, London and Glasgow Group D, Bilbao and Dublin Group E, with Munich and Budapest the Group F venues.