This story has been updated.
Pataki first announced his White House run in a campaign video released Thursday morning.
"America has a big decision to make about who we're going to be and what we're going to stand for. The system is broken," Pataki said in the video, which emphasized his leadership following the 9/11 terrorist attacks. "The question is no longer about what our government should do, but what we should do about our government, about our divided union, about our uncertain future."
Pataki, who has not held elected office since 2007, is the eighth Republican presidential contender to enter the race so far.
Pataki had flirted with a presidential candidacy three times before this year, raising money and meeting voters in early-voting states such as New Hampshire. But each time -- in 2000, in 2008 and in 2012 -- Pataki decided the moment wasn't right, and he never launched a campaign.
“I make a joke that every four years, there’s the Olympics, there’s the World Cup, and I come to New Hampshire thinking about running for president,” Pataki told a crowd of 15 people during a speech at a Sea-Doo and snowmobile dealership in Laconia, N.H., last month.
[Flashback: Will he or won't he? (He will.)]
Now that Pataki has actually entered the race, he must face the harsh reality that flirting had allowed him to avoid. Which is that he has very little chance of winning the GOP nomination. "I understand I have a long uphill fight to even become the Republican nominee," he recently acknowledged to NH1 News.
On Thursday, he said his time had come. “I’m ready. I know that the need to change Washington is as big as been in my lifetime. I know the need to have a vision for the future of this country is absolutely essential. I have that vision. My life has prepared me for this moment,” he told The washington Post and NH1.
For one thing, he will enter an already crowded GOP field without the benefit of name recognition. This January on "Jeopardy," three contestants were shown a photo of Pataki's face -- but none could remember his name. Last month, when he shook hands with patrons in a New Hampshire Chipotle, many said afterward that they had no idea who he was.
And Pataki's moderate record in New York -- strong gun-control laws, an expansion of the state budget -- does not seem well-suited to today's GOP primary voters.
In the most recent Fox News poll of GOP primary voters nationwide, Pataki's support had fallen from its previous high -- 1 percent. Now, Pataki's support was so low it didn't register in the poll, putting him in a tie for last place in a 16-person field. ("None of the above" out-performed Pataki, getting 3 percent.)
If Pataki were to win the 2016 Republican nomination, Florida-based GOP strategist Rick Wilson said a few weeks ago, “basically, it would be like a monkey flying out of a unicorn’s [posterior].”
Still, Pataki believes he has a chance. He does have a base of longtime donors in New York. And Pataki has pulled off a political upset before. In 1994, the relatively unknown Republican unseated Gov. Mario Cuomo (D), a liberal icon, in one of the most famous races in New York political history.
But that was merely an upset. This would be closer to a miracle. In this election, Pataki's plan to surge from the back of the GOP pack will rely heavily on the televised debates -- in which Pataki hopes to stand out as statesmanlike. If he can get on the stage at all.
Pataki's 2016 strategy is also heavily dependent on New Hampshire. Pataki has visited the Granite State at least nine times in this election cycle and hopes that the state's socially moderate voters will help him surprise the GOP establishment on primary day.
Even in New Hampshire, Pataki is way behind at the moment. The WMUR Granite State poll, carried out by the University of New Hampshire, found him tied with Louisiana Gov. Bobby Jindal for 12th place among likely GOP primary voters.
But the news in New Hampshire wasn't all bad. The same poll showed that, after nine trips to New Hampshire, Pataki's support is growing.
In February, Pataki got only 1 percent in the WMUR poll.
This month, it was up to 2 percent.
Jose A. DelReal and NH1 Political Director Paul Steinhauser contributed to this report.