Former “Sex and the City” star Cynthia Nixon made it official on Monday — she will take on Gov. Cuomo in September’s Democratic primary.

The lefty actress, who had been flirting with a bid for months, released a slick online video that announced her candidacy — and took plenty of digs at Cuomo.

“New York is my home. I’ve never lived anywhere else,’’ Nixon says in the video, which included her and her wife, education activist Christine Marinoni, and the actress’s three children.

“But something has to change,’’ Nixon, 51, says against a backdrop of gray, blighted streets.

“Our leaders are letting us down,” she says. “We are sick of politicians who care more about headlines and power than they do about us. It can’t just be business as usual anymore.”

Describing the governor as a “centrist and insider,’’ Nixon added that Cuomo has “been defined by a string of indictments for corruption,” failed to fix the subways and is in cahoots with the GOP through a “backroom deal” that allows them to control the state Senate.

Her celebrity status — Nixon played the sensible Miranda on the hit HBO series — immediately paid off in terms of publicity for her campaign.

News of the actress’s first bid for political office dominated the Internet and was trending on Facebook and Twitter.

Former “SATC” co-star Kristin Davis, who portrayed conservative Charlotte, added to the star power, tweeting, “I am so proud of @cynthiaNixon . . . I know she would be an excellent Governor !’’

Davis, asked by The Post whether she would campaign for Nixon, responded that she “will support her in every and any way she needs me.’’

Nixon has signed up former top campaign aides to Mayor de Blasio — a staunch Cuomo foe — to help run her race. Her treasurer is Zephyr Teachout, who ran a strong but losing campaign against Cuomo in 2014.

The actress’ political bid won raves from leaders of the leftist New York Progressive Action Network, which indicated that it will likely endorse her.

“It’s a great day for democracy. It’s a great day for the progressive moment,” said NYPAN co-Chairman George Albro, whose group includes many progressive Democrats who backed Bernie Sanders for president in 2016.

Veteran political consultant Hank Sheinkopf said Nixon could provide Cuomo with a spirited primary.

But echoing a new poll Monday that showed Cuomo trouncing Nixon, Sheinkopf said the governor will still prevail.

“Nixon has a lot of access to money and angry people who don’t like Cuomo. But it’s next to impossible to beat an incumbent governor in the primary,’’ Sheinkopf told The Post.

Still, he said, Cuomo will have to careful in the way he criticizes Nixon.

“You can’t run a traditional negative campaign against a woman in this ‘Me Too’ moment,” he said.

Last week, the governor had called Nixon a second-rate celebrity with no political chops.

A Cuomo campaign spokesman said in a statement Monday, “It’s great that we live in a democracy where anyone can run for office.’’

Additional reporting by Kate Sheehy