Officer Amber Guyger had been dismissed after nearly five years on the job for her actions on the night of the shooting earlier in September, Dallas Police Chief U. Renee Hall said in a statement. Hall also said Guyger had engaged in "adverse conduct" when she was arrested for manslaughter, without elaborating.
Guyger, 30, had been on administrative leave since she fatally shot Botham Jean, 26. The killing of an unarmed black man by a white officer sparked protests in the Texas city, with many calling for the officer to be fired and charged with murder.
Dallas Mayor Mike Rawlings said he heard the calls to take action and supported the decision.
"The swift termination of any officer who engages in misconduct that leads to the loss of innocent life is essential if the Dallas Police Department is to gain and maintain the public trust," he said in a statement.
A funeral for Jean was planned for Monday in his native Saint Lucia, Dallas media reported.
S. Lee Merritt, an attorney for the Jean family, said the police chief informed the family of the department's decision on Sunday night and they supported the move.
"The Jean family said that this was an initial victory but are still focused on the proper indictment by the grand jury of murder, a successful prosecution, and an appropriate sentence," he said in an interview. The family is also considering suing the department and the city, he said.
The case is before a grand jury. District Attorney Faith Johnson said the panel may decide to uphold the manslaughter charge on which Guyger was arrested, or it could consider a more serious charge of murder.
Police said Guyger has told investigators she mistook Jean's residence for her own and shot him, believing he was an intruder.
Guyger said she had mistakenly gone to Jean's apartment one floor above her own and managed to enter because the door was slightly ajar, according to an arrest warrant affidavit.