The local school board voted unanimously to fire Pete Arredondo, who had been on leave since June.
His lawyers said in a written statement that he had been unaware anyone was inside the classrooms with the shooter.
The firing came three months to the day since the attack and two weeks before the new school term begins.
The attack at Robb Elementary School on 24 May was the deadliest US school shooting in nearly a decade.
Many parents and relatives have expressed deep anger at the police response and there has been growing pressure for law enforcements to be held accountable.
Mr Arredondo has taken the brunt of criticism for officers’ 77-minute delay in confronting the teenage gunman, and is the first officer to be dismissed.
Cheering was heard in the auditorium as Uvalde Consolidated Independent School District’s board of trustees filed the motion to remove him from his post immediately.
As Wednesday evening’s meeting began, some in the audience shouted: “Coward!”
School pupil Caitlin Gonzalez, who survived the shooting, said her message for Mr Arredondo was: “Turn in your badge and step down.”
Lawyers for Mr Arredondo – who was not at the meeting – called him “a courageous officer” and his firing “an unconstitutional public lynching”.
They said their client, who had led the small police force since 2020, did not think he was the official in charge at the time of the attack.
In a 17-page statement reported by the Austin American-Statesman newspaper, the attorneys maintained: “Chief Arredondo did the right thing.
“Any allegation of lack of leadership is wholly misplaced.”
The statement also said the school district had failed to carry out any investigation “establishing evidence supporting a decision to terminate” his client.
And it added that Uvalde school officials had put Mr Arredondo’s safety at risk by refusing to allow him to carry a weapon to the school board meeting if he were to have attended.
It continued: “The complaint that an officer should have rushed the door, believed to be locked, to open it up without a shield capable of stopping an AR-15 bullet, without breaching toolsâ€¦ is tantamount to suicide.”
But an inquiry heard in June that the classroom door was not locked and there was no evidence officers tried to open it.
Labelling the response an “abject failure”, Mr McCraw also said Mr Arredondo had “decided to place the lives of officers before the lives of children”.
Mr McCraw’s department is also under scrutiny – it had more than 90 state troopers at the scene of the massacre.
Among the parents at Wednesday’s meeting was Ruben Torres, father of Chloe Torres, who survived the shooting.
“Right now, being young, she is having a hard time handling this horrific event,” said Mr Torres, a former US Marine.
School officials have said that students will not be sent back to Robb Elementary School when term begins on 6 September and will instead be provided with temporary classrooms elsewhere in Uvalde or virtual schooling.
Mr Arredondo stepped down in July from a city council seat he won shortly before the school shooting, amid angry calls for him to lose that post, too.