Brian Mulheren, a veteran detective who as an audacious, deft and indefatigable one-man emergency management liaison between City Hall and the New York Police and Fire Departments became known as “Mr. Disaster” and the “Night Mayor,” died on Sunday at a hospice in Miami. He was 73.

The cause was chronic obstructive pulmonary disease, said his nephew Charles J. Ott, a retired police sergeant, who attributed the condition to Mr. Mulheren’s exposure to debris at the World Trade Center site after the terrorist attack in 2001.

Mr. Mulheren played an outsize role for a first-grade detective. He was armed with a gold shield, but his uniform, such as it was — it typically consisted of a rumpled beige trench coat and a crumpled Irish tweed hat — was devoid of the stars and bars that define status on the police force.

Yet by sheer force of personality and the connections he had cultivated, he was deferred to by city commissioners and by police supervisors who outranked him when he arrived, often first, at the scene of a crisis in his black Lincoln Town Car, which was crowned with a forest of antennas that linked him to every emergency radio frequency in the city,

In the 1970s and ’80s, he served as City Hall’s wake-up call when an officer was shot or a firefighter was felled. Before the city established a full-fledged emergency management department, he seamlessly and almost single-handedly coordinated interagency strategies.

“He was one of those rare people who kept the N.Y.P.D. and the Fire Department together,” John Miller, the Police Department’s deputy commissioner for intelligence and counterterrorism, said in an interview. “He basically created the organized response to chaos that we replicated and have used ever since.”

He was also recognized as a guardian angel to emergency workers who were injured in the line of duty.

Mr. Mulheren was credited by Officer Steven McDonald’s family with saving his life when he was shot in Central Park by a teenage bicycle thief in 1986 and rushed in a patrol car to Metropolitan Hospital, where doctors said he was unlikely to survive.

In 2016, Mr. McDonald told Columbia, the Knights of Columbus magazine, that he vividly remembered Mr. Mulheren’s dauntless intervention.

“You might think he’s not going to make it, but we’re going to Bellevue,” Mr. Mulheren announced on his own initiative, according to “New York’s Finest,” a forthcoming book by Michael Daly.

“He had no rank or high station but stepped forward and said, ‘No, he’s not going to die; he just needs a second chance,’” Mr. McDonald recalled. “I believe that was the Holy Spirit speaking through Brian to everyone there. Just like that like they loaded me up on a special ambulance and flew down to Bellevue Hospital, where they saved my life by the grace of God.”

Mr. McDonald, who remained paralyzed from the neck down, became a champion of forgiveness, even expressing hope for his assailant’s redemption. He died in 2017 but lived to see his son, Conor, promoted to detective by Commissioner William J. Bratton and assigned shield No. 97, the number that had belonged to Mr. Mulheren until he retired.

Mr. Mulheren’s indomitable spirit derived largely from the personal relationships he developed and from his record of intolerance for red tape, which became the stuff of legend.

In another emergency, when a firefighter was overcome and no ambulance was immediately available, Mr. Mulheren was said to have commandeered a city bus, told the passengers to debark and ordered the driver to take the injured man to the hospital.

Serving mostly under Mayors John V. Lindsay, Edward I. Koch and David N. Dinkins, Mr. Mulheren, a police buff since childhood, insinuated himself into the department’s decisions to buy smaller patrol cars to economize on gas; change their color from green, black and white in the early 1970s to “grabber blue” with white accents to make them more visible and less intimidating; modernize lights and sirens; air-condition the cars; and improve radio communications. He also encouraged the Fire Department to requisition a hyperbaric oxygen therapy chamber to treat burn victims.

In his book “A Mayor’s Life: Governing New York’s Gorgeous Mosaic” (2013), Mr. Dinkins described Mr. Mulheren as a “quirky” detective who was “something of a personal emergency management unit.”

Brian Francis Mulheren was born on Nov. 29, 1947, in Manhattan to Joseph Mulheren, a representative for the Consolidated Edison power company, and Mary (McCaughern) Mulheren, a homemaker.

He is survived by his sister, Elizabeth Ott. A brother, Joseph, died before him.

After graduating from DeWitt Clinton High School in the Bronx, he joined the Police Department in 1968. He worked as a detective in the Bronx and was assigned to a surveillance unit and deployed in the Office of Management Analysis and Planning and the commissioner’s office. Shortly after he retired in 1996, he moved to Florida, where he remained engaged in civic affairs as a member of the Bal Harbour Citizens Coalition.

Despite more than two decades of distinguished, if unconventional, service, he ended his tenure in the department on a sour note after years of vexing hidebound bureaucrats and department brass.

In 1992, his Lincoln was wrecked in an accident that he said occurred while he was chasing a suspect’s getaway car. After years of litigation, he finally received a disability pension. Separately, he was cleared in a departmental disciplinary proceeding that raised questions about whether he had been on the job at the time of the accident.

Testifying on his behalf at that proceeding, John F. Timoney, the chief of the department, said unequivocally of Mr. Mulheren, “I have never known him to be off duty.”