Calling it the "honour of a lifetime," Massachusetts Sen. Elizabeth Warren said on Thursday she is ending her bid for the Democratic nomination for president.

Warren, who electrified progressives with her "plan for everything" and strong message of economic populism, confirmed earlier to her campaign staff she would depart the race.

Speaking to reporters outside her home in Cambridge, Mass., said she would continue fighting in her current capacity for everyday Americans "who have gotten the short end of the stick."

"There are still tens of millions of people across the country who, one bad medical diagnosis and they're upside down financially. There are still mamas and daddies all across this country who can't finish their education, can't take on jobs because they can't find access to decent child care that they can afford," Warren said, standing beside her husband Bruce Mann.

For much of the past year, her campaign had all the markers of success: robust poll numbers, impressive fundraising and a sprawling political infrastructure that featured staffers on the ground across the country. She was squeezed out, though, by Bernie Sanders, who had an immovable base of voters she needed to advance.

"I refuse to let disappointment blind me — or you — to what we've accomplished," Warren told her campaign staff on a conference call. "We didn't reach our goal, but what we have done together — what you have done — has made a lasting difference. It's not the scale of the difference we wanted to make, but it matters."

Warren never finished higher than third in the first four states and was routed on Super Tuesday, failing to win any of the 14 states voting and placing an embarrassing third in her home state, behind former vice-president Joe Biden and Sanders.

Members of the Biden and Sanders campaigns confirmed Thursday that Warren had reached out to them, but there were no further details on that front from Warren herself.

"Let's take a deep breath and spend a little time on that," she told reporters. "We don't have to decide that this minute."

Warren, 70, entered the race on Feb. 9, 2019 in her home state of Massachusetts, but wasn't able to translate some strong debate performances into delegates.

Her polling began improving through the summer and she appeared to further hit her stride as she hammered the idea that more moderate Democratic candidates, including Biden, weren't ambitious enough to roll back harmful policies of Donald Trump's administration.

Warren of Massachusetts is shown Feb. 26 campaigning in South Carolina. She finished third in her home state on Super Tuesday, and only amassed a few dozen delegates across the 14 states voting. (Matt Rourke/The Associated Press)

Warren's exit from the race following Minnesota Sen. Amy Klobuchar's departure the past week leaves the Democratic field with just one female candidate: Hawaii congresswoman Tulsi Gabbard, who has collected only one delegate toward the nomination. It was an unexpected twist for a party that had used the votes and energy of women to retake control of the House of Representatives.

Warren said she appreciated it was "going to be hard" for many women and girls to have to wait at least four more years to see a female president.

Took on big tech, Wall Street

Warren had a compelling message, calling for "structural change" to the American political system to reorder the nation's economy in the name of fairness, in particular targeting Wall Street and Silicon Valley giants over their enormous influence and power. She had a signature populist proposal for a two per cent wealth tax she wanted to impose on households worth more than $50 million US that prompted chants of "Two cents! Two cents!" at rallies across the country.

"I'm not somebody who has been looking at myself in the mirror since I was 12 years old saying, 'You should run for president,"' Warren said aboard her campaign bus on the eve of the New Hampshire primary.

"I started running for office later than anyone who is in this, so it was never about the office — it was about what we could do to repair our economy, what we could do to mend a democracy that's being pulled apart. That's what I want to see happen, and I just want to see it happen."

Warren was struggling after early voting. But many observers felt she damaged the aspirations of Democratic candidate Mike Bloomberg in his first appearance on the debate stage, on Feb. 19 in Las Vegas. (John Locher/The Associated Press)

Warren's poll numbers began to slip after a series of debates when she repeatedly refused to answer direct questions about if she'd have to raise taxes on the middle class to pay for Medicare for All. Her top advisers were slow to catch on that not providing more details looked to voters like a major oversight for a candidate who proudly had so many other policy plans.

When Warren finally moved to correct the problem, her support eroded further. She moved away from a full endorsement of Medicare for All, announcing that she'd work with Congress to transition the country to the program over three years. In the meantime, she said, many Americans could "choose" to remain with their current, private health insurance plans, which most people have through their employers. Biden and other rivals pounced, calling Warren a flip-flopper, and her standing with progressives sagged.

After Super Tuesday narrowed the field to two front-runners, Joe Biden and Bernie Sanders, who showcase the two sides of the Democratic party. 2:52

Warren got a foil for all of her opposition to powerful billionaires when former New York mayor Mike Bloomberg entered the race. During a debate in Las Vegas just before Nevada's caucus, Warren hammered Bloomberg and the mayor's lacklustre response touched off events that ended with him leaving the race on Wednesday.

For Warren, that led to a sharp rise in fundraising, but didn't translate to electoral success.

Born in Oklahoma to a churchgoing Methodist family, the former Harvard law professor was registered as a Republican until changing affiliation in 1996.

Warren raised her national profile with appearances as a personal finance expert on Dr. Phil beginning in 2003. She was soon tapped by Democratic leadership and the Barack Obama administration, serving on a congressional panel evaluating government bailout programs and then serving in the Consumer Financial Protection Bureau.

Elizabeth Warren has dropped out of the Democratic presidential race, telling reporters she needs more time to decide who she will endorse. Warren drew praise for her debate performances, but it didn't translate into votes in the primaries. 5:02

Encouraged to run for office, in November 2012 she toppled Scott Brown, the Massachusetts senator once thought to be a rising star in the Republican Party.

Warren said she was a former candidate with no regrets.

"Ten years ago I was teaching a few blocks from here and talking about what was broken in America and ideas for how to fix it, and pretty much nobody wanted to hear it. I've had a chance to get out there and talk to millions of people and we have ideas now that we talk about that we just weren't talking about even a year ago."

Leaving the scrum with her husband as well as her golden retriever, Bailey, she was met with boisterous applause from supporters.