He guided the Raptors to a 13-4 record in November. Toronto posted six straight wins from Nov. 15-26 and reached the top spot in the conference standings for the first time in 10 years.
Casey is the first coach in team history to win the award on two occasions. He also earned the honour in December 2013.
David Joerger of the Memphis Grizzlies was named Western Conference coach of the month.
Casey joined the Raptors as head coach in June 2011 and led the team to a franchise-record 48 wins last season.
Lenny Wilkens (April 2002) and Sam Mitchell (January 2007) are the only other Toronto coaches who have won the award.