[1] Shelbourne were confirmed Champions and promoted to the League of Ireland Premier Division on 1 October 2021.
Shelbourne and Cork City joined following their relegation from the Premier League at the end of the 2020 season.
[5][4] On 10 November 2020 a newly formed Limerick based club Treaty United announced that they would apply for a 2021 League of Ireland licence.
[6] Former Dublin based League of Ireland club St Francis FC and Wexford based Yola FC also both expressed interest in joining for 2021 by the deadline for expressions of interest which was 10 November 2020.
[8] Note: Flags indicate national team as has been defined under FIFA eligibility rules.