Deputies responded to the casino located on the 45000 block of Pechanga Parkway around 11 p.m., and found a man suffering from gunshot wounds in the lobby of the casino.
Police say the victim entered the lobby of the casino following the shooting to seek emergency medical treatment.
He was transported to Temecula Valley Hospital where he succumbed to his injuries.
A female, associated with the victim, was located in a guest room at the casino suffering from non-life threatening injuries.
The victims' identities have not been released.
Deputies say no suspects are outstanding, and that the shooting stemmed from a domestic violence incident. No further details were released.
The investigation is ongoing. Anyone with any information regarding this incident was urged to contact Investigators Bowen of the Sheriff's Central Homicide Unit at (951) 955-2777 or Investigator Devine of the Sheriff's Southwest Station at (951) 696-3000.