The Southern League is an amateur status league competition organized by New Zealand Football but run by Mainland Football and Southern Football for Association football clubs located in the South Island of New Zealand. It is at the second level of New Zealand Football behind the national association based New Zealand National League, and the highest level of club based football available to teams within the region.
In March 2021, New Zealand Football announced a change to the structure of both the premiership and the top regional leagues around the country. The four top regional leagues (NRFL Premier, Central Premier League, Mainland Premier League and the FootballSouth Premier League) would be formed into the Northern League, Central League, and the Southern League. These leagues would allow local clubs to qualify for the premiership season (now known as the National League Championship), with the top 4 teams from the Northern League, the top 3 teams from the Central League, and the top 2 teams from the Southern League making up the competition, alongside the Wellington Phoenix Reserve side. All teams that qualify plus the Phoenix Reserves, would then play a single round-robin competition between September and December. For the Southern League, the two existing competitions run in the South Island (Mainland Premier League and FootballSouth Premier League) play their original league seasons for the teams to then qualify for a place in the newly formed competition. Five teams from Mainland Premiership, which covers the top of the South Island to Christchurch and three teams from FootballSouth Premier League, covering from below Christchurch to the bottom of the South Island, will qualify. The competition will start on the 17 July 2021.