League A consists of the top 12 ranked UEFA members, split into four groups of three. The winners of each group will advance to the UEFA Nations League Finals, and the third-placed team of each group will be relegated to the 2020–21 UEFA Nations League B.
The Nations League Finals will take place in June 2019 and be played in a knockout format, consisting of the semi-finals, third place play-off, and final. The semi-final pairings, along with the administrative home teams for the third place play-off and final, are determined by means of a draw on 3 December 2018. The host country will be selected among the four qualified teams on 3 December 2018 by the UEFA Executive Committee, with the winners of the final crowned as the inaugural champions of the UEFA Nations League.
The four group winners will be drawn into groups of five teams for the UEFA Euro 2020 qualifying competition (in order to accommodate for the Nations League Finals). In addition, League A will be allocated one of the four remaining UEFA Euro 2020 places. Four teams from League A which have not already qualified for the European Championship finals will compete in the play-offs, to be played in March 2020. The play-off berths will be first allocated to the group winners, and if any of the group winners have already qualified for the European Championship finals, then to the next best ranked team of the league, etc. If there are fewer than four teams in League A which have not already qualified for the European Championship finals, the play-off berths will be allocated to the next best ranked team of the following league, etc. The play-offs will consist of two "one-off" semi-finals (best-ranked team vs. fourth best-ranked team and second best-ranked team vs. third best-ranked team, played at home of higher-ranked teams) and one "one-off" final between the two semi-final winners (venue drawn in advance between semi-final 1 and 2).
Teams were allocated to League A according to their UEFA national team coefficients after the conclusion of the 2018 FIFA World Cup qualifying group stage on 11 October 2017. Teams were split into three pots of four teams, ordered based on their UEFA national team coefficient. The seeding pots for the draw were announced on 7 December 2017.
The prize money to be distributed was announced in March 2018. Each team in League A will receive a solidarity fee of €1.5 million. In addition, the four group winners will receive double this amount via a €1.5M bonus fee.
The four group winners of League A, which will participate in the Nations League Finals, will also receive the following fees based on performance:
Third place: €2.5M
Fourth place: €1.5M
This means that the maximum amount of solidarity and bonus fees for a team from League A is €7.5M.
The four best teams in League A according to the overall ranking that have not qualified for UEFA Euro 2020 through the qualifying group stage will compete in the play-offs, with the winners qualifying for the final tournament. If there are fewer than four teams in League A that have not qualified, the remaining slots are allocated to teams from another league, according to the overall ranking.