UPDATE, 11:49 a.m ET: From msnbc's Aliyah Frumin: Romney’s decision to not seek the presidency a third time is being seen as a win for establishment candidates, including New Jersey Gov. Chris Christie and former Florida Gov. Jeb Bush – who would potentially be vying for the same pool of mainstream GOP cash.
Several donors previously told msnbc in the fall that they were waiting to see what Romney would do before they aligned themselves with another candidate.
Both Christie and Bush have both recently announced that they are setting up committees to explore potential 2016 bids. The New York Times reported on Friday that Romney is scheduled to have dinner on Friday, suggesting Romney is considering backing the Garden State governor should he jump into the race.
UPDATE: 11:08 a.m. ET: Romney has spoken to supporters on a conference call, reading a statement explaining his decision. "It is best to give other leaders in the party the opportunity to become our next nominee," he said. "I believe that one of our next generation of Republican leaders, one who may not be as well known as I am today, one who has not yet taken their message across the country, one who is just getting started, may well emerge as being better able to defeat the Democrat nominee. In fact, I expect and hope that to be the case."
UDPATE, 11:00 a.m. ET: NBC News has confirmed that Mitt Romney will NOT run for the Republican nomination in 2016. The news was first reported by radio talk show host Hugh Hewitt.
UPDATE, 10:12 a.m. ET: NBC News political director Chuck Todd confirms Romney will host two calls Friday -- one for a small group of close advisers and one for a broader group of supporters and donors. Word of the two calls was first reported by ABC News.
UPDATE, 9:49 a.m. ET: NBC News political director Chuck Todd threw cold water on speculation that Romney would announce moves toward a 2016 bid Friday, tweeting that Romney supporters are saying they don't believe the former presidential candidate will run again.
UPDATE, 9:08 a.m. ET: A Romney source told msnbc they've seen "no indication really" from Mitt's circle that he's considering pulling the plug, nor has there been an obvious downside to a 2016 run that's been weighing heavily on discussions. The source said Romney has shown a burning "belief that he's right for the job" that's been the dominant factor in driving the revival of his campaign, would be hard to turn off.
Mitt Romney held an 11 a.m. call with supporters on Friday and discussed his 2016 presidential intentions. Close Romney supporters received an email asking them to join the call.
The 2012 Republican presidential nominee and his wife, Ann, have been deliberating over a third run for the White House, and have privately said they'll make the decision in short order.
Romney has told backers he would make income inequality a central theme of his campaign if he decides to run again. It's a big change from 2012, when President Obama's re-election team successfully painted Romney, a multimillionaire former private equity executive, as out of touch with the concerns of the middle class.
At an event Thursday night with House Democrats, Obama chided Romney as a "former presidential candidate" who is "suddenly deeply concerned about poverty." Romney shot back in a tweet, scolding the president for "the record number of poor in your term."
Romney, a former two-term Massachusetts governor, has been phoning donors and other GOP operatives in recent weeks to assess his chances in a crowded field of other likely GOP hopefuls. Former Florida Gov. Jeb Bush is actively exploring a possible bid and on Thursday locked up a former top Romney aide, Iowa GOP strategist David Kochel, as a senior adviser. Others considering a run include Wisconsin Gov. Scott Walker, New Jersey Gov. Chris Christie, and Sens. Marco Rubio of Florida, Ted Cruz of Texas and Rand Paul of Kentucky.
Romney and his wife are also expected to attend a luncheon in New York City with Chelsea Clinton and her husband on Friday, shortly after the planned 11 a.m. call with supporters, at an event to benefit the Ann Romney Center for Neurological Diseases Brigham and Women's Hospital in Boston. Chelsea's mother, former Secretary of State Hillary Rodham Clinton, is the odds-on favorite to win the Democratic presidential nomination next year.
Romney was badly hurt in his 2012 bid after a tape surfaced where he appeared to dismiss 47% of the electorate as unwilling to vote for him because they depended on government benefits.
This is a developing story and will be updated.