The Eurostadium in Brussels was due to host four group matches and one Last 16 game, but it won't be ready in time so those matches have been reassigned to Wembley Stadium in London.
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.
The decision means that Wembley will stage seven games in total - the final, both semi-finals, a last-16 match and three group games - resulting in the biggest festival of worldwide football in the country since Euro 96.
Wembley, which has hosted the Champions League final twice in the last seven years, was already set to stage the final and semi-finals of Euro 2020, which were assigned in 2014.
Despite being in the running as alternative options, Cardiff's Principality Stadium and Stockholm's Friends Arena missed out on the chance to replace Brussels.
UEFA also announced that Rome's Stadio Olimpico would host the opening match. "We absolutely need a new 45,000-seat stadium and we hope that the competent ministers will grant the permit in January so that a stadium for the 21st century can finally be built in our country".
In response to the decision, the Football Association of Wales (FAW) said they were "extremely disappointed" and have written to UEFA for an explanation.
UEFA President Aleksander Čeferin said they had not addressed when construction would start and it would therefore be too much of a risk for the continental body for Brussels to remain as a host city.
"The concept of Euro 2020 to 13 different countries was devised to allow smaller countries, like Wales, to have a unique opportunity of being involved in staging a major tournament", it said.
The 2020 tournament is the first to be played under a new format with group games spread across several countries.
Matches in Group C are scheduled to be held at the Krestovsky Stadium in Saint Petersburg, a venue for the 2018 World Cup, and the Parken Stadium in Copenhagen.
And if England qualify for the tournament, they will play at least two group-stage games at Wembley, just as Ireland and Scotland will get two home games if they reach the tournament.