The 1989 New Zealand National Soccer League was the 20th season of a nationwide round-robin club competition in New Zealand football. Napier City Rovers had their debut championship win over Mount Maunganui, in doing so taking the title away from the main centres for only the second time.
At the end of the 1988 season two teams were relegated: Manawatu United finished last, and Nelson United were expelled for failing to meet NZFA ground criteria.
Traditionally, their places would have been taken by the top ranked teams in a play-off between the winners of the northern, central, and southern regional leagues. In 1989, however, this did not happen. Although Takapuna City finished top in the Northern League, a new composite team was promoted from that region, Waitakere City. This team was formed as a composite team consisting of several West Auckland teams (Te Atatu, Massey, Kelston West, and West Auckland), all of whom continued to keep their own sides as feeder clubs for the new team. The top ranked Central League team was also promoted, Waterside Karori, a team which had formed from the merger of former =national league team Waterside and Karori Swifts. The Southern league champions were the Christchurch United B side, who were not eligible for entry to the national league.
Papatoetoe were relegated at the end of the 1989 season.
The 1989 season was unique for the number of matches that had their results altered due to league rule infringements. Three matches had their results changed after the fact: Miramar Rangers' 1–1 home draws with Christchurch United and Hutt Valley United were both revised to 0–1 away wins, and Gisborne City's 2–2 draw at home with Manurewa was similarly amended to a 0–2 result. These three results took the tally in the leagues first twenty years to four amended results in total.