After registering low poll numbers and failing to qualify for the third round of primary debates, he suspended his campaign on September 20, 2019, and endorsed Bernie Sanders five months later.

[24] After returning from Nicaragua, de Blasio moved to New York City, where he worked for a nonprofit organization focused on improving health care in Central America.

[27] In 1997, he was appointed to be the regional director for the United States Department of Housing and Urban Development (HUD) for New York and New Jersey under the administration of President Bill Clinton.

As the tri-state region's highest-ranking HUD official, de Blasio led a small executive staff and took part in outreach to residents of substandard housing.

[37] During his tenure, the General Welfare Committee also passed the Benefits Translation for Immigrants Law, which helped non-English speakers receive free language-assistance services when accessing government programs.

The New York Times endorsed de Blasio, praising his efforts to improve public schools and "[help] many less-fortunate New Yorkers with food stamps, housing, and children's health" as a councilmember.

The paper declared de Blasio the best candidate for the job "because he has shown that he can work well with Mayor Bloomberg when it makes sense to do so while vehemently and eloquently opposing him when justified.

[49] In June 2010, de Blasio opposed a New York City Housing Authority decision to cut the number of Section 8 vouchers issued to low-income New Yorkers.

"[51] De Blasio has criticized Citizens United, the January 2010 U.S. Supreme Court decision that overturned parts of the 2002 McCain–Feingold Bipartisan Campaign Reform Act.

[58] The Democratic primary race included nine candidates, among them Council Speaker Christine Quinn, former U.S. Representative Anthony Weiner, and former New York City Comptroller and 2009 mayoral nominee Bill Thompson.

Celebrities such as Alec Baldwin and Sarah Jessica Parker endorsed him, as did prominent politicians such as former Vermont Governor Howard Dean and U.S. Congresswoman Yvette Clarke.

[62] De Blasio gained media attention during the campaign when he and a dozen others, including city councillor Stephen Levin, were arrested while protesting the closing of Long Island College Hospital.

[66] In September 2013, de Blasio voiced his opposition to charter schools, maintaining that their funding saps resources from classes like art, physical education and after-school programs.

[71] On September 16, second-place finisher Bill Thompson conceded, citing the unlikelihood of winning a runoff even if uncounted absentee and military ballots pushed de Blasio below the 40% threshold.

[82] In July 2014, de Blasio signed a bill authorizing the creation of municipal identification cards for all residents regardless of immigration status, to help secure access to city services.

[94] Atlantic Avenue, in the East New York neighborhood of Brooklyn, which has been scarred by decades of poverty and crime, was the first test and focus of de Blasio's strategy on affordable housing, one of the policy initiatives central to his platform of reducing inequality.

The agreement created "specific requirements and milestones to address the serious health and safety hazards at NYCHA properties, including lead-based paint, mold, heat, vermin, among others".

"[98][103] On March 16, The New York Times reported that during the previous week, de Blasio's "top aides were furiously trying to change the mayor's approach to the coronavirus outbreak.

There had been arguments and shouting matches between the mayor and some of his advisers; some top health officials had even threatened to resign if he refused to accept the need to close schools and businesses."

[114] In April 2019, De Blasio announced his support for the Green New Deal and for legislation to ban the construction of glass and steel skyscrapers in New York City, citing environmental concerns and feeling they contribute to global warming.

[120] On February 14, 2019, while addressing a rally in New York City about combating antisemitism, De Blasio said: "Maybe some people don't realize it, but when they support the BDS movement, they are affronting the right of Israel to exist and that is unacceptable.

[122] In December 2018, De Blasio announced his support for marijuana legalization in New York City, calling it a "once-in-a-generation opportunity to get a historic issue right for future New Yorkers.

[124] In 2015, de Blasio repealed a public health requirement that mohels inform parents of the risks of metzitzah b'peh, an oral circumcision ritual that was linked to 17 cases of infant herpes, brain damage, and two deaths since 2000.

[127] After de Blasio installed allies and donors on New York City's Board of Health, a new policy was instated that mohels could be banned for life if they tested positive for herpes and the DNA strain matched the infant's, but only after a child was infected.

[139] In February 2014, Pastor Bishop Orlando Findlayter—the founder of the New Hope Christian Fellowship Church, and a friend and supporter of de Blasio—was pulled over for failing to signal before making a left turn.

[143] De Blasio also "offered qualified support for protesters after the grand jury decision not to charge the officer involved in the chokehold death of Eric Garner in New York City".

[144] After New York City police officers Wenjian Liu and Rafael Ramos were killed in an ambush in December 2014, "cops and union leaders publicly rebuked [de Blasio], arguing [that] his earlier remarks had stoked anti-police sentiment.

[145][146] In November 2019, de Blasio criticized former mayor Michael Bloomberg's apology for the stop and frisk policy, tweeting, "This is LONG overdue and the timing is transparent and cynical.

Some of the ideas brought up in the report were to rebuild Penn Station/Madison Square Garden, create more bus rapid transit routes,[157] and a "Vision Zero" initiative to reduce traffic-related deaths in the city.

[189] In July 2023, de Blasio and McCray announced their separation and that they will start dating other people, though the two would not be seeking a divorce and would continue to share their Park Slope residence.