The 46 AFC member associations (excluding the associate member Northern Mariana Islands) were ranked, based on their national team's and clubs' performance over the last four years in AFC competitions, with the allocation of slots for the 2019 and 2020 editions of the AFC club competitions determined by the 2017 AFC rankings (Entry Manual Article 2.3):
For the 2019 AFC Champions League, the associations were allocated slots according to their association ranking which was published on 15 December 2017, which took into account their performance in the AFC Champions League and the AFC Cup, as well as their national team's FIFA World Rankings, between 2014 and 2017.
The following 51 teams from 22 associations entered the competition.
In the following table, the number of appearances and last appearance count only those since the 2002–03 season (including qualifying rounds), when the competition was rebranded as the AFC Champions League. TH means title holders.
In the qualifying play-offs, each tie was played as a single match. Extra time and penalty shoot-out were used to decide the winner if necessary (Regulations Article 9.2). The eight winners of the play-off round (four each from both West Region and East Region) advanced to the group stage to join the 24 direct entrants. All losers in each round from associations with only play-off slot entered the AFC Cup group stage.
The bracket of the qualifying play-offs for each region, determined based on the association ranking of each team, with the team from the higher-ranked association hosting the match, was officially announced by the AFC prior to the group stage draw on 22 November 2018. Teams from the same association could not be placed into the same tie.
The draw for the group stage was held on 22 November 2018, 16:30 MYT (UTC+8), at the AFC House in Kuala Lumpur, Malaysia. The 32 teams were drawn into eight groups of four: four groups each in the West Region (Groups A–D) and the East Region (Groups E–H). Teams from the same association could not be drawn into the same group.
The teams were ranked according to points (3 points for a win, 1 point for a draw, 0 points for a loss). If tied on points, tiebreakers were applied in the following order (Regulations Article 10.5):
Goals scored in head-to-head matches among tied teams;
Away goals scored in head-to-head matches among tied teams;
If more than two teams were tied, and after applying all head-to-head criteria above, a subset of teams were still tied, all head-to-head criteria above were reapplied exclusively to this subset of teams;
Goal difference in all group matches;
Goals scored in all group matches;
Penalty shoot-out if only two teams playing each other in the last round of the group were tied;
Disciplinary points (yellow card = 1 point, red card as a result of two yellow cards = 3 points, direct red card = 3 points, yellow card followed by direct red card = 4 points);
In the round of 16, the winners of one group played the runners-up of another group from the same region, with the group winners hosting the second leg, and the matchups determined by the group stage draw.
The draw for the quarter-finals was held on 2 July 2019. In the quarter-finals, the four round of 16 winners from the West Region (whose identity was not known at the time of the draw) played in two ties, and the four round of 16 winners from the East Region played in two ties, with the matchups and order of legs decided by draw, without any seeding or country protection.
In the semi-finals, the two quarter-final winners from the West Region played each other, and the two quarter-final winners from the East Region played each other, with the order of legs determined by the quarter-final draw.
In the final, the two semi-final winners played each other, with the order of legs (first leg hosted by team from the West Region, second leg hosted by team from the East Region) reversed from the previous season's final.