A longtime associate of President Trump’s family, who organized golf tournaments on the president’s courses and planned his son Eric’s wedding, will soon oversee billions of federal dollars as the head of the Department of Housing and Urban Development’s New York and New Jersey office.

Lynne Patton had been working as a senior adviser and director of public engagement at HUD for several months before Ben Carson, the department secretary, recommended her for the new role, a person close to Mr. Carson said. Before that, Ms. Patton had no experience in housing policy.

The appointment of a Trump family loyalist to a key government post fits a pattern. His daughter Ivanka and son-in-law, Jared Kushner, work in White House offices. Dan Scavino Jr., who was the president’s caddie, is the director of social media. His longtime bodyguard, Keith Schiller, has become such an important White House figure that he hand-delivered the dismissal papers for James Comey, the former F.B.I. director, to the bureau’s headquarters.

Nonetheless, the appointment of Ms. Patton elicited incredulous responses in New York.

“Like many things in the Trump universe, we’re dealing with things we’ve never seen before,” Mayor Bill de Blasio, who held the same post during the Clinton administration, said in a weekly radio interview on WNYC. “Folks in that role historically have had substantial background in government or in housing.”