The Dallas Police Department said in a statement that Guyger was sacked after an internal investigation concluded she had engaged in "adverse conduct".
It's not clear what "adverse conduct" the department means.
A lawyer for Botham Jean's family says they are considering suing the police department and the city.
The statement says she was sacked for "her actions", but does not elaborate on those actions.
Lee Merritt, an attorney for Jean's family, also slammed the investigation into the shooting, saying officials were seeking evidence to discredit Jean. Following the completion of the Texas Rangers' and the Dallas County District Attorney's Office's investigations in the case, it will be up to a grand jury to decide whether to indict Guyger for murder, manslaughter or not at all.
Barrick Gold agrees to buy rival Randgold in all-share deal
Under the all-share deal, Randgold shareholders would be given 6.1280 shares in the combined company for each share they own. Barrick's more stable North American assets will reduce Randgold investors' exposure to risky African markets.
Botham Jean was scheduled to be laid to rest in his native St. Lucia on Monday.
There are conflicting narratives over what led up to the shooting.
Guyger had recently ended a 15-hour shift when she returned in uniform to the South Side Flats apartment complex.
She had said the door was ajar, but opened under the force of her unique door key, which is outfitted with an electronic chip, the documents said. When she opened the door, she saw the interior was almost completely dark, according to the affidavit.
Guyger said she concluded her apartment was being burglarized and gave verbal commands to the person, who ignored them. She turned on the lights while on the phone with 911, and only when asked for her address did she realize she was in the wrong apartment, she told police. She then drew her weapon and fired twice at Jean, the affidavit said.
However, for many, the decision is almost three weeks too late, eroding an already tumultuous relationship between law enforcement and vulnerable communities that have been disproportionally impacted in police shootings. Authorities have not released results.
The decision to fire Guyger came after an internal review, which Guyger can appeal the decision, police said.