Guyger was sacked during a hearing Monday, Hall said.
"An Internal Affairs investigation concluded that on September 9, 2018, Officer Guyger, #10702, engaged in adverse conduct when she was arrested for manslaughter", the statement read.
Guyger was arrested on a manslaughter charge after she shot and killed Jean earlier this month. Inside, the lights were off, and she saw a figure in the darkness that cast a large silhouette across the room, according to the officer's account.
The search warrant affidavit - written by a Dallas police detective before the Rangers were handed the case - also says that Jean's door was open when Guyger inserted a key but that Jean "confronted the officer at the door".
She called 911 and, when asked where she was, returned to the front door to see she was in the wrong unit, according to the affidavit. The Dallas County District Attorney's office is also conducting its own investigation.
Jean grew up in the Caribbean island nation of St. Lucia before attending college in Arkansas.
She drew her weapon and fired, killing Jean, an employee of accounting firm PricewaterhouseCooper.
Jean wasn't the first person shot by Guyger. Its conclusions were discussed during a hearing on Monday, and "Officer Guyger was terminated for her actions".
On Sept. 14, protesters rallied from the Dallas Police Department, near the apartments where Guyger shot Jean, to downtown.
"We not asking anyone to jump to any conclusions", attorney Lee Merrit said in a press conference the day before Guyger's arrest.
Guyger, who was hired by the department in November 2013, had been assigned to the city's Southeast Patrol Division.
Guyger reportedly moved out of the Southside Flats apartment complex - located just blocks away from Dallas police headquarters - last week.