The officer was identified as Erik Andrade by Milwaukee police chief Alfonso Morales during a speech at Marquette University on Thursday, according to the Milwaukee Journal Sentinel's Ashley Luthern and Mary Spicuzza.
Morales revealed Andrade was terminated for violating social media policy, not for his role in the arrest, which saw Brown tased and tackled by 11 officers for double-parking across two handicap spots.
Andrade mocked Brown on his social media account shortly after the arrest, stating it was "nice meeting" Brown in the lot of a local Walgreens.
"This is unfortunate ... firing somebody is very serious in a profession such as this," said Morales, who was afraid Andrade's social media use would come back to haunt him in court. "But at the same time for me, one of the most important functions of a police officer is to be able to testify in court."
"And if you can't testify in court ... then I can't utilize you."
Brown filed a federal civil rights suit against the Milwaukee Police Department in June for unlawful arrest and excessive force.