Ronnie O'Sullivan was the defending champion, having won his sixth world title at the previous year's event, where he defeated Kyren Wilson 18–8 in the final.

The 32 players for the event are selected through a mix of the snooker world rankings and a pre-tournament qualifying stage.

[5] As of 2022[update], Stephen Hendry and Ronnie O’Sullivan are the event's most successful participants in the modern era, having both won the championship seven times.

[6][7] The 2020 championship had been won by English player Ronnie O'Sullivan, who defeated compatriot Kyren Wilson in the final 18–8 to win his sixth world title.

[8][9][10] The event was returned to its traditional April schedule after the 2020 championship was delayed to late July because of the COVID-19 pandemic.

[15] It was the 45th consecutive year that the tournament had been held at the Crucible, and the 53rd successive world championship to be contested through the modern knockout format.

[22][23] Other international broadcasts were provided by Kuaishou, Migu, Zhibo.tv, Youku, and CCTV in China; by NowTV in Hong Kong; and by DAZN in Canada, the United States, and Brazil.

[24] On 13 March 2021, World Snooker announced that the championship would welcome a limited number of spectators, as part of the Events Research Programme run by the British government in response to the ongoing COVID-19 pandemic.

[25] Details were announced on 7 April, beginning with an audience of 33 per cent of the arena's full capacity for the first round, an increasing number of spectators through the tournament, and a full-capacity crowd to be admitted for the final.

[30] The defeat for White meant he was not ranked high enough to remain on the World Snooker Tour, but he was later given an invitational place for the following two seasons.

[31] Three-time World Championship semi-finalist Alan McManus announced his retirement after his second-round loss to Bai Langning.

[33] Four players were competing having started in the opening round: Bai Langning, Jamie Clarke, Igor Figueiredo, and Steven Hallworth,[33] but all four lost their final qualifying match.

[40] Joyce won the first frame in the second session, but O'Sullivan took the next to lead 7–4 and then scored three century breaks of 124, 137, and 112 to win the match 10–4.

[45] Jamie Jones had returned to the tour for the 2020–21 season, having lost his professional status in 2019 after serving a year-long ban for contravening betting regulations.

[48] The previous year's semi-finalist Anthony McGill led Ricky Walden 5–4 in the first session, and won five of the next six to win 10–5.

When interviewed afterwards, he admitted that Carter was the "worst draw" but added: "I've never won a tournament so why not make the World Championship the first one?

"[56][57] Mark Allen defeated Lyu Haotian, having led 7–2 after the first session and then winning three straight frames to take the match 10–2.

[64] Three-time champion Mark Williams trailed 0–2 at the start of his match against Sam Craigie, but won five of the next seven frames to take a 5–4 lead.

[65] The 2005 champion Shaun Murphy trailed 3–5 in his match against Mark Davis, but won the final frame of the first session with a break of 113.

[66] Murphy credited this century for giving him additional motivation for the second session as he won six of the eight frames to seal a 10–7 victory.

O'Sullivan made breaks of 81, 105 and 138 to lead 4–1, but McGill won the final three frames to tie the match 4–4 after the first session.

[86] Murphy faced the last Chinese player remaining, Yan, and won the opening session 6–2, making the highest break of the tournament, a 144.

[118] In the fourth session, Selby tied the score by winning the opening two frames, before Bingham won the next to lead 14–13.

[111][121] This match was more than three and a half hours longer than the other semi-final, in part due to extended safety play and two frames having to be restarted twice.

[125] Selby then won four of the next five frames to end the second session 10–7 ahead, as Murphy failed to pot a ball for an hour.

[130] After Murphy missed a pot on a red down the cushion in frame 33, Selby cleared the table to win the match 18–15.

[124][131][132] This was Selby's fourth championship, behind only Hendry (with seven), Steve Davis, Ray Reardon, and Ronnie O'Sullivan (each with six) in the modern era, and equal with John Higgins.

[12][137] † = Winner of frame Qualifying for the main stages of the tournament took place between 5 and 14 April 2021 at the English Institute of Sport in Sheffield.

The WPBSA selected 16 amateur players to participate in the qualifying rounds together with the 112 professionals outside the top 16 of the world rankings.

[13] Antoni Kowalski and Wu Yize were initially invited, but withdrew and were replaced by Hamim Hussain and Julien Leclercq.