The 51-year-old declared her candidacy with a two-minute campaign video posted on Twitter that showed her at home with her wife and children, riding the subway, taking one of her children to school and speaking at liberal political causes.
The move confirmed speculation that Nixon would challenge incumbent Democratic Governor Andrew Cuomo. If elected, Nixon -- who is a vocal opponent of President Donald Trump -- would be New York state's first woman and first openly gay governor.
The actress and liberal activist, who has campaigned for gay marriage, public schools and access to women's health care, announced that she was "sick of politicians who care more about headlines and power than they do about us."
"Our leaders are letting us down. We are now the most unequal state in the entire country with both incredible wealth and extreme poverty. Half the kids in our upstate cities live below the poverty line. How did we let this happen?" she said in the video.
"Something has to change. We want our government to work again -- on health care, ending mass incarceration, fixing our broken subway.
"Together we can win this fight," finished the New York-born and raised Nixon, who said she grew up with her mother in what she called "a one-bedroom, fifth-floor walkup."
The Trump presidency has seen a surge in women -- particularly Democratic women -- running for office. Only eight of the current 50 US state governors are women.
In 2004, Nixon accepted an Emmy award -- the highest accolade in US television -- for her role as Miranda Hobbes from Trump, the fellow celebrity-turned-politician whose current presidency she publicly opposes.
New York, the fourth most populous state in the United States, goes to the polls to elect a governor on November 6. But Nixon remains a left-field candidate with Cuomo very much the favored contender ahead of the Democratic Party primary on September 13.
Despite the stardom brought by her role alongside Sarah Jessica Parker on the hit HBO comedy from 1998-2004 that spawned two movies, a recent Siena College poll found that Cuomo is overwhelmingly favored by Democrats to Nixon by 66 to 19 percent.
The governor, who is seeking his third term, has downplayed the competition and Nixon has never previously run for office.
"I'm not nervous about whoever runs," Cuomo said last week. "They'll be people who run. That's called elections and that's fine."
Considered a potential Democratic presidential candidate for 2020, Cuomo is shored up by a bevvy of powerful supporters, but it remains unclear whether he will be badly damaged by the recent conviction of a close friend and aide for bribery.
According to The New York Times, Cuomo's name was mentioned 163 times during Joseph Percoco's eight-week federal trial.
Nixon, who is close to left-leaning New York Mayor Bill de Blasio, echoes some of the language used by 2016 Democratic Party presidential contender Bernie Sanders, who electrified the left before ultimately losing to Hillary Clinton.
Her campaign fundraising page stipulates that she "won't be accepting any corporate contributions" and that "instead our campaign will be powered by the people."
If Trump has proved a celebrity can win office as a political novice, the mother-of-three is far from the first US actor to venture into politics.
Republican president Ronald Reagan got his political start after acting as a two-term governor of California from 1967 to 1975. Arnold Schwarzenegger, the Austrian-born body builder, also served as California governor from 2003-2011.
And Former television comic Al Franken -- for whom Nixon once campaigned -- was Democratic senator of Minnesota from 2009 until early this year, when he was forced to step down over sexual misconduct allegations.//AFP