Rudy Giuliani during the September 11 attacks

In the wake of the attacks, Giuliani was hailed by many for his leadership during the crisis. When polled just six weeks after the attack Giuliani received a 79% approval rating among New York City voters, a dramatic increase over the 36% rating he had received a year earlier — seven years into his administration.[23][24]

In his public statements, Giuliani mirrored the emotions of New Yorkers after the September 11 attacks: shock, sadness, anger, resolution to rebuild, and the desire for justice to be done to those responsible. "Tomorrow New York is going to be here", he said. "And we're going to rebuild, and we're going to be stronger than we were before...I want the people of New York to be an example to the rest of the country, and the rest of the world, that terrorism can't stop us."[25] Giuliani was widely praised by some for his close involvement with the rescue and recovery efforts, but others, including many police, rescue workers, and families of WTC victims argue that "Giuliani has exaggerated the role he played after the terrorist attacks, casting himself as a hero for political gain."[26]

As an avid and public fan of the New York Yankees, who won four World Series Championships during his time as mayor, Giuliani was frequently sighted at Yankee games, often accompanied by his son. On September 21, 2001, the first game was played in New York City after the attacks, with the New York Mets at home facing the Atlanta Braves. Despite his being a Yankee fan, the crowd cheered for him and for his leadership over the preceding days.[27]

The term "America's Mayor", now in common usage among Giuliani supporters, was coined by Oprah Winfrey at a 9/11 memorial service held at Yankee Stadium on September 23, 2001.[18][28]

The 9/11 attack occurred on the scheduled date of the mayoral primary to select the Democratic and Republican candidates to succeed Giuliani. The primary was immediately delayed two weeks to September 25. During this period, Giuliani sought an unprecedented three-month emergency extension of his term, from its scheduled expiration on January 1 to April 1, due to the circumstances of the emergency besetting the city.[29] He threatened to challenge the law imposing term limits on elected New York City officials and run for another full four-year term, if the primary candidates did not consent to permit the extension of his mayoralty.[30]

Advocates for the extension contended that Giuliani was needed to manage the initial requests for funds from Albany and Washington, speed up recovery, and slow down the exodus of jobs from lower Manhattan to outside New York City.

Although a provision for emergency extensions is written into the New York State Constitution (Article 3 Section 25),[31] in the end leaders in the State Assembly and Senate indicated that they did not believe the extension was necessary.[32] The election proceeded as scheduled, and the winning candidate, the Giuliani-endorsed Republican Michael Bloomberg, took office on January 1, 2002 per normal custom.

On December 24, 2001,[33] Time magazine named Giuliani its Person of the Year for 2001.[34] Time observed that, prior to 9/11, the public image of Giuliani had been that of a rigid, self-righteous, ambitious politician. After 9/11, and perhaps owing also to his bout with prostate cancer, his public image had been reformed to that of a man who could be counted on to unite a city in the midst of its greatest crisis. Thus historian Vincent J. Cannato concluded in September 2006, "With time, Giuliani's legacy will be based on more than just 9/11. He left a city immeasurably better off — safer, more prosperous, more confident — than the one he had inherited eight years earlier, even with the smoldering ruins of the World Trade Center at its heart. Debates about his accomplishments will continue, but the significance of his mayoralty is hard to deny."[35]

Giuliani has been subject to increased criticism for downplaying the health effects of the air in the Financial District and lower Manhattan areas in the vicinity of the Ground Zero.[36] He moved quickly to reopen Wall Street, and it was reopened on September 17. He said, in the first month after the attacks, "The air quality is safe and acceptable."[37] However, in the weeks after the attacks, the United States Geological Survey identified hundreds of asbestos hot spots of debris dust that remained on buildings. By the end of the month the USGS reported that the toxicity of the debris was akin to that of drain cleaner.[38] It would eventually be determined that a wide swath of lower Manhattan and Brooklyn had been heavily contaminated by highly caustic and toxic materials.[38][39] The city's health agencies, such as the Department of Environmental Protection, did not supervise or issue guidelines for the testing and cleanup of private buildings. Instead, the city left this responsibility to building owners.[38]

Firefighters, police and their unions, have criticized Giuliani over the issue of protective equipment and illnesses after the attacks.[36] An October 2001 study by the National Institute of Environmental Safety and Health said that cleanup workers lacked adequate protective gear.[40][41] The Executive Director of the National Fraternal Order of Police, Sally Regenhard, reportedly said of Giuliani: "Everybody likes a Churchillian kind of leader who jumps up when the ashes are still falling and takes over. But two or three good days don't expunge an eight-year record."[42] she went on to say, "There's a large and growing number of both FDNY families, FDNY members, former and current, and civilian families who want to expose the true failures of the Giuliani administration when it comes to 9/11." She told the New York Daily News that she intends to "Swift Boat" Giuliani.[43]

A May 14, 2007 New York Times article, "Ground Zero Illness Clouding Giuliani's Legacy," gave the interpretation that thousands of workers at Ground Zero have become sick and that "many regard Mr. Giuliani's triumph of leadership as having come with a human cost." The article reported that Giuliani seized control of the cleanup of Ground Zero, taking control away from experienced federal agencies, such as the Federal Emergency Management Agency, the Army Corps of Engineers and the Occupational Safety and Health Administration. He instead handed over responsibility to the "largely unknown" city Department of Design and Construction. Documents indicate that the Giuliani administration never enforced federal requirements requiring the wearing of respirators. Concurrently, the administration threatened companies with dismissal if cleanup work slowed.[44] The New York Times faulted his decision-making on the post September 11 cleanup of the World Trade Center site, in the lead editorial of the May 22, 2007 issue. Additionally, the Times took Giuliani to task for his handling of worker safety at the site and the issue of first responder health problems.[45]

Giuliani wrote to the city's Congressional delegation and urged that the city's liability for Ground Zero illnesses be limited, in total, at $350 million. Two years after Giuliani finished his term, the Federal Emergency Management Agency (FEMA) appropriated $1 billion to a special insurance fund to protect the city against 9/11 lawsuits.[46]

In 2007, then-Senator Hillary Clinton contemplated calling Giuliani to testify before a Senate committee on whether the government failed to protect recovery workers from the effects of polluted Ground Zero air.[47][48]

Matt Taibbi wrote an article for the June 14, 2007 issue of Rolling Stone, blaming Giuliani for rushing the recovery effort and setting a poor example for recovery workers.[49]

In June 2007, former Republican Governor of New Jersey and director of the Environmental Protection Agency Christie Whitman reportedly stated that the EPA had pushed for workers at the WTC site to wear respirators but that she had been blocked by Giuliani. She stated that she believed that the subsequent lung disease and deaths suffered by WTC responders were a result of these actions.[50] Former deputy mayor Joe Lhota, who had by then joined Giuliani's presidential campaign, replied, "All workers at Ground Zero were instructed repeatedly to wear their respirators." A safety professional who worked at Ground Zero added, "I was absolutely aghast at the refusal of the workers at ground zero to wear the personal protective equipment. All of my efforts to convince these guys to wear the masks was for naught."[51]

In February 2007, the International Association of Fire Fighters issued a letter accusing Giuliani of "egregious acts" against the 343 firemen who had died in the September 11th attacks. The letter asserted that Giuliani rushed to conclude the recovery effort once gold and silver had been recovered from World Trade Center vaults and thereby prevented the remains of many victims from being recovered: "Mayor Giuliani's actions meant that fire fighters and citizens who perished would either remain buried at Ground Zero forever, with no closure for families, or be removed like garbage and deposited at the Fresh Kills Landfill," it said, adding: "Hundreds remained entombed in Ground Zero when Giuliani gave up on them."[52] Lawyers for the International Association of Fire Fighters seek to interview Giuliani under oath as part of a federal legal action alleging that New York City negligently dumped body parts and other human remains in the Fresh Kills Landfill.[47]

A book later published by Commission members Thomas Kean and Lee H. Hamilton, Without Precedent: The Inside Story of the 9/11 Commission, maintained that the Commission had not pursued a tough enough line of questioning with Giuliani when he appeared before the Commission, because its members were afraid of public outcry.[53] Family members had interrupted the proceedings, demanding an explanation from Giuliani for the lack of working radios. Some were removed from the hearing.[53] The Commission had experienced criticism the morning of Giuliani's testimony for allegedly implying that police and firefighters had not done their jobs properly with their hard questions directed to some of Giuliani's staff the previous day. Commission member John Lehman had said that New York City's disaster planning was "not worthy of the Boy Scouts, let alone this great city."[53] The morning of Giuliani's testimony, the New York Post ran a picture of a New York firefighter with the headline "Insult" in response to Lehman's statement.[53]

Some family members of 9/11 victims have openly criticized Giuliani for the significant communication failures that occurred on that day, believing that the lack of working walkie-talkies put the lives of first responders in significant danger. They say that the lack of radios had been a complaint of emergency services responders for years but was never dealt with and led to deaths of first responders in building collapses for which they should have been warned.[54] In December 2006, Sally Regenhard, mother of firefighter Christian Regenhard who died on September 11, and co-founder of the Skyscraper Safety Campaign, vowed to expose the truths of Giuliani's actions on 9/11 before 2008, stating, "I can't see why any 9/11 family member who knows the truth about the failures of the Giuliani administration ... would not be outraged."[55] She said in April 2007, "The bitter truth is that Rudy Giuliani is building a path to the White House over the bodies of 343 firefighters."[54]

By April 2007 it was reported that Giuliani had been forced to limit his appearances in New York City due to the increasing protests by family members of 9/11 victims, particularly police, fire and other emergency workers.[54]