De Blasio, who launched his campaign with a video in which he pledged to “put working people first,” vowed to “keep speaking up for working people.”
His departure comes as recent polls have shown three candidates — former vice president Joe Biden, Sen. Bernie Sanders (I-Vt.) and Sen. Elizabeth Warren (D-Mass.) — significantly ahead of their rivals.
De Blasio, who failed to qualify for the third Democratic debate last week in Houston, joined the race in May. A September poll of New York showed zero percent support in his home state, and he has lagged in national polling as well.
During his MSNBC appearance, de Blasio said he was not ready to endorse any of his fellow Democrats but said he would support the party’s eventual nominee.
“Whoever’s the nominee, I’m going to be there for them,” said de Blasio, who won his second term as mayor of the country’s biggest city in 2017.
“I would say there’s some very good candidates,” de Blasio said of those remaining in the field. “I actually think this is one of the, you know, most impressive fields we, as Democrats, have had in a long time.”
De Blasio is the sixth Democratic candidate to exit the race since July. Others who have dropped out include Rep. Eric Swalwell (Calif.), former Colorado governor John Hickenlooper, Washington Gov. Jay Inslee, Rep. Seth Moulton (Mass.) and Sen. Kirsten Gillibrand (N.Y.).
President Trump was quick to weigh in on de Blasio’s departure, posting a sarcastic tweet.
“Oh no, really big political news, perhaps the biggest story in years!” Trump wrote.
He later mocked de Blasio while speaking to reporters in the Oval Office.
“He only had one real asset,” Trump said of de Blasio. “You know what it was? Height. Other than that, he had nothing, though.”
In an opinion piece posted Wednesday morning on an NBC News website, de Blasio argued that Democrats “must return to our roots as a party focused on bold solutions that speak to the concerns of working people.”
“If we do not, we will lose in 2020,” he said. “Yes, Donald Trump lies to working people, but he at least pretends to talk to them. That may be enough for him to win, if we do not constantly make it clear that the Democrats are the party of everyday Americans in rural counties and urban centers, the coasts and the heartland.”
De Blasio also vowed to “redouble my efforts to improve the quality of life of everyday New Yorkers.”
Michael Scherer contributed to this report.