- Source: 2021 RFL League 1 results
The fixture list for the 2021 season was issued on 14 February 2021. The regular season comprised 18 rounds.
The end-of-season play-offs featured the clubs finishing second to sixth in the regular season in a four round elimination competition to decide which team accompanied the team finishing first into the Championship for 2022.
Four matches were postponed due under the RFL COVID-19 protocols and were not rearranged.
All times are UK local time (UTC+1) on the relevant dates.
Regular season
= Round 1
== Round 2
== Round 3
== Round 4
== Round 5
== Round 6
== Round 7
== Round 8
== Round 9
== Round 10
== Round 11
== Round 12
== Round 13
== Round 14
== Round 15
== Round 16
== Round 17
== Round 18
=Play-offs
Workington Town, who finished the regular season in second place, advanced straight to the qualifying semi-final in the second week of the play-offs. Teams that finished 3rd to 6th after the regular season played off in qualifying and elimination play-offs respectively. Keighley Cougars defeated North Wales Crusaders in the qualifying play-off and proceeded to the qualifying play-off against Workington Town, where they lost. Doncaster defeated Hunslet in the elimination play-off which resulted in the latter being eliminated from the play-offs. Doncaster then proceeded to defeat North Wales in the elimination semi-final which saw them advance to the preliminary final against Keighley.