The sport of professional snooker has had a world ranking system in place since 1976. Certain tournaments were given ranking status, with the results at those events contributing to a player's world ranking. The events that made up the 1976–77 snooker season were the first to use ranking points, awarding points from earlier seasons. Originally, the world rankings were decided based only on results in the World Snooker Championship, but other events were later added. The system used for the 2020–21 snooker season was first used in the 2010–11 season, where players were awarded ranking points based entirely on prize money won from these events. The rankings are based on the prior two seasons, with ten revisions after specific tournaments throughout the season. These revisions are used as official rankings, with points awarded in the current season overwriting those from two years prior.
Judd Trump began the season as the world number one and retained the position throughout, as he won five ranking events. Trump began the season with a lead of over 500,000 points, ahead of 2020 World Snooker Championship winner Ronnie O'Sullivan in second, and finished the season in first, above 2021 World Snooker Championship winner Mark Selby by 124,000 points.
Ranking list Revision dates Seedings for each event were based on the world rankings, with totals being updated at specific revision dates. On these dates, ranking points from the 2018–19 snooker season were removed from a player's total.
+Revision dates Revision point Date After 2018/2019 points dropped1 28 September 2020 European Masters Riga MastersWorld OpenPaul Hunter Classic 2 31 October 2020 Championship League China ChampionshipEuropean MastersEnglish OpenInternational Championship 3 23 November 2020 Northern Ireland Open Northern Ireland Open 4 7 December 2020 UK Championship UK Championship 5 21 December 2020 World Grand Prix Scottish Open 6 8 February 2021 Shoot Out German MastersWorld Grand PrixShoot Out 7 22 February 2021 Welsh Open Welsh Open 8 29 March 2021 Tour Championship Indian OpenPlayers ChampionshipGibraltar OpenChina OpenTour Championship Total 4 May 2021 World Championship World ChampionshipSources:
Seeding list The following table contains the rankings which were used to determine the seedings for following tournaments. Other provisional and unofficial rankings are produced after each ranking event which are not noted here. Blank fields indicate that the player was not active on the tour, or had no ranking. The names are initially sorted by the scores at the end of the season.