Bayern Munich defeated Paris Saint-Germain in the final, played at the Estádio da Luz in Lisbon, Portugal, 1–0 and became the first European Cup winners to win all their matches during the tournament.

[5] In keeping with its introduction the campaign prior, the video assistant referee (VAR) system was in use from the play-off round onwards.

[9] Apart from the allocation based on the country coefficients, associations could have additional teams participating in the Champions League, as noted below: The following is the access list for this season.

In any case where a spot in the Champions League was vacated, teams of the highest-ranked associations in earlier rounds of the appropriate path were promoted accordingly.

[10] The schedule of the competition was as follows (all draws were held at the UEFA headquarters in Nyon, Switzerland, unless stated otherwise).

[12] A working group was set up by UEFA to decide the calendar of the remainder of the season.

[13] On 17 June 2020, UEFA announced the revised schedule for the quarter-finals, semi-finals and final of the competition, to be played in single-leg matches.

All of the four matches in the first week of fixtures went ahead but due to the increased severity of the COVID-19 pandemic in Spain and France, Valencia's and PSG's home games were played behind closed doors.

[14][15] On 15 March, UEFA announced a halt to the competition meaning that the remaining second leg games would be postponed indefinitely.

The draw for the group stage was held on 29 August 2019, 18:00 CEST, at the Grimaldi Forum in Monaco.

In the knockout phase, teams played against each other over two legs on a home-and-away basis, except for the one-match final.

[32] On 17 June 2020, UEFA announced that due to the COVID-19 pandemic in Europe, the final stages of the competition would feature a format change: the quarter-finals, semi-finals and final would be played in a single-leg format from 12 to 23 August 2020 at the Estádio da Luz and Estádio José Alvalade in Lisbon, Portugal.

Due to concerns over the COVID-19 pandemic in Europe, the second set of second leg matches were postponed by UEFA on 13 March 2020.

[16] On 17 June 2020, UEFA announced that the second legs would be played on 7–8 August 2020, with the venue to be decided between the home team's stadium and a neutral stadium in Portugal (at the Estádio do Dragão in Porto and the Estádio D. Afonso Henriques in Guimarães).

[35] On 9 July 2020, UEFA announced that the remaining second legs would be held at the venues originally proposed.

[36] The first leg of the Atalanta v Valencia tie was retrospectively blamed by local civic and medical authorities for contributing to the extremely high concentration of coronavirus cases in Atalanta's home city of Bergamo.

[37][38][39] The second leg of the Atlético Madrid v Liverpool tie was similarly blamed for the sharp increase in coronavirus-related deaths in North West England.

[46] The award winners were announced and presented during the 2020–21 UEFA Champions League group stage draw in Switzerland on 1 October 2020.