They sat 13th in the Eastern Conference this season with a 15-36 record at the time of his departure. "We thank Steve for his many years of service to our organization and look forward to continuing our relationship with him as part of our board".
ESPN's Ramona Shelburne and Adrian Wojnarowski report that Dolan is considering a front office model that is similar to the ones that are in place with the Warriors and Lakers - two teams that have former player agents running their basketball operations departments.
The Knicks said it was anticipated that Mills would be nominated to the board of MSG's standalone sports company following the completion of the proposed spinoff of the entertainment business. Mills lasted 2 1/2 years as team president, but in that time, the Knicks were spurned by every A-list free agent despite playing in the league's biggest market.
Pressure shifted onto Mills after Fizdale was sacked following a 4-18 start to his second season.
A statement from the Knicks said: "The New York Knicks today announce that Steve Mills will be leaving his position as president of the New York Knicks, effective immediately". Fizdale was 21-83 in less than two seasons as Knicks coach.
Mills, 60, has served as the Knicks' president since July 2017.
The Knicks are owned by the Dolan-led Madison Square Garden Company (MSG), the organisation behind the eponymous midtown NY arena.
Whoever replaces Mills has another key offseason approaching.
Wojnarowski adds that Knicks owner Jim Dolan is targeting Toronto Raptors president Masai Ujiri to ultimately oversee New York's operations.
The GM doesn't have a guaranteed contract for next season, so he's likely toast whenever a new president comes aboard.
Another reason to make the Mills' move now instead of after the season ends is to do research on other possible candidates outside Ujiri and traditional GMs currently employed.