They also fired top assistant Keith Smart.
Miller previously served as head coach of the Westchester Knicks, the team's G League affiliate, from 2015 through his promotion to the New York staff in August. He led Westchester to a 108-92 record and three postseason appearances, winning the 2017-18 G League Coach of the Year Award.
The 55-year-old Illinois native owns three decades of coaching experience at the college and professional levels. He served as head coach at Texas State (1994-2000) and Eastern Illinois (2005-12), compiling a 162-209 record across 13 seasons with one NCAA tournament berth.
New York holds the second-worst record in the league at 4-18 and has lost eight games in a row.
The roster doesn't feature enough established talent to seriously compete in the star-oriented NBA after the front office whiffed on the biggest targets on the free-agent market over the summer.
A coaching change won't magically turn the Knicks into title contenders, but Fizdale's squad didn't show signs of progress while posting a 21-83 record across the past season and a quarter.
Miller and Co. will attempt to get the best out of a promising young core led by RJ Barrett, Kevin Knox and Mitchell Robinson with help from veterans Marcus Morris Sr. and Julius Randle.
Widespread changes to the roster, coaching staff and front office could be on the horizon at season's end if the Knicks continue to lag behind in the Eastern Conference.