Eva Moskowitz, the polarizing charter school chief who has frequently clashed with Mayor Bill de Blasio, will not run for mayor in 2017, she said Thursday.

Speaking in front of City Hall, Moskowitz said she wanted to remain focused on her growing network of charter schools and on “educational activism.” The much-anticipated announcement brings speculation about her role in the 2017 mayor’s race to an early end, though she said she hasn’t ruled out a run in 2021.

“I think that what could be accomplished in public education is game changing,” she said. “I believe we have the chance to dramatically change public education, of doing for education, frankly, what Apple did with computing for the iPhone, what Google is doing with driverless cars.”

With Moskowitz bowing out of the mayoral race, speculation is likely to shift to the question of whether she will give her blessing to another candidate — which could bring with it the backing of thousands of charter-school parents and perhaps some of Success’ wealthy financiers. She said Thursday that she would seek to endorse a candidate who promised to overhaul the city’s education system, but added that she has yet identify that person.

Moskowitz has developed a passionate, if still relatively small, constituency of parents who want to see charter schools expand. On Wednesday, thousands of charter school supporters marched to City Hall, including parents, students, and teachers from Success’ nearly three-dozen schools.

But she would have faced a tough challenge if she had decided to face off against de Blasio when he runs for a second term: The mayor would have an advantage as an incumbent with broad support among organized labor, and Moskowitz would need to cultivate a larger base of support beyond charter-school parents and donors.

She also would have to contend with a reputation for abrasiveness and a record of confrontation with her critics, which has led some fellow charter operators to distance themselves from her and galvanized many charter-school opponents. During her announcement Thursday, protesters chanted in nearby City Hall Park.

Moskowitz acknowledged that such protests would become a fact of life if she became mayor, with “four years of dueling press conferences” likely between her administration and her chief antagonist, teachers union president Michael Mulgrew.

Mulgrew released a statement after the press conference suggesting that if Moskowitz ran for mayor it would expose her connection to big donors.

“Thousands of teachers and parents are disappointed today.  They had been looking forward to pulling back the curtain and showing the public the real Eva Moskowitz and the privatization agenda of her hedge-fund pals,” he said.

Still, the interest her announcement brought on Wednesday and Thursday illustrates the power she wields as one of de Blasio’s toughest critics. Moskowitz defeated the mayor early in his tenure when he tried to block her schools from moving into public buildings, and she has more recently publicized their disputes over payments and public space for her schools. On Thursday, she said she does not blame him for the challenges facing the city school system, but that he should be held accountable for finding ways to fix it.

Moskowitz, a former city councilwoman who chaired the education committee, has long mixed politics with the work of running charter schools. She runs a political action committee, Great Public Schools, that’s given money to Gov. Andrew Cuomo and other state elected officials in recent years. She’s also an adept fundraiser, with members of the Success Academy network’s board contributing large sums to campaigns.

Her decision not to challenge de Blasio comes as Success Academy is growing quickly. The network is preparing to open eight new schools next year, and dozens of others are still expanding. The network also saw the departures of two longtime executives last month, including Keri Hoyt, Moskowitz’s longtime second-in-command.

One challenge for Moskowitz, and Success, if she were to run for public office in the future is the scrutiny it would attract to her schools.

Moskowitz has clashed with educators on a host of practices that she uses in her schools — whose students consistently outscore most of their charter and traditional school peers on state tests — including harsh discipline policies. She says that suspensions should be used to send a message to students and families about a school’s expectations, something she’s defended as many cities, and federal education officials, have pushed to reduce exclusionary discipline practices. Her schools have also been criticized for an overemphasis on intense test preparation and for serving a smaller share of high-needs students than the traditional public school system.

Meanwhile, Moskowitz’s appearances in Washington and at education-reform events have given her a growing profile on the national stage. Last year, she testified before Congress about education’s role in boosting the economy and this year brought students and a teacher to Capitol Hill to show demonstrate a lesson to lawmakers.

“I am very clear in my convictions of what needs to be done,” she said Thursday, “so I’m going to continue to do educational activism in the same way I’ve done it for the last 20 years.”