Officer Brad Miller lost his job because of the August 7 incident at a car dealership in Arlington, Police Chief Will Johnson told reporters.
"Based on a preponderance of evidence available to me and the facts revealed by the investigative team, I have decided to terminate Officer Miller's employment with the Arlington Police Department for exercising poor judgment," Johnson said.
The officer was in the last stages of his field training when he shot Christian Taylor, 19, multiple times at a car dealership.
A security company called 911 after Taylor allegedly drove his SUV through the front window of the dealership showroom. When officers arrived, Taylor was inside. Authorities have said that he did not comply with initial calls to surrender.
Miller entered the building alone. He reportedly told investigators he feared that he would be overpowered by Taylor, who was moving quickly toward him while cursing. Miller was later joined inside the building by his training officer, a 19-year veteran. Miller fired four times and the other officer used a Taser.
There was no physical contact between Taylor and the officers.
"This unilateral decision to enter the building and to continue the pursuit deeper into the building upon making contact with Mr. Taylor -- along with failing to communicate with fellow officers or develop an arrest plan -- created an environment of cascading consequences that produced an unrecoverable outcome," Johnson said about Miller's decision.
He stressed that a separate criminal investigation is ongoing. Once that work is complete, all reports will be submitted to the Tarrant County district attorney for consideration and submission to the grand jury.
"The grand jury will decide if the use of force in this incident rises to the level of criminal prosecution," Johnson said.
Taylor played defensive back at Angelo State University. Last year's roster listed him as a 5-foot-9, 180-pound freshman.
His father has said while it appears his son did wrong, he shouldn't have had to die.
"What he'd done, ain't no way right," Adrian Taylor told CNN affiliate KTVT.
"But to shoot an unarmed man? You're a police officer, you're trained to take down men with your hands. You have your Tasers, you have your clubs, whatever there is. Unarmed, a 19-year-old -- and you shoot to kill?"