Ms. Wiley, one of the more left-leaning candidates in the race, said she had heard from Mr. Jeffries on Friday night, adding that he, along with Ms. Clarke and Ms. Velázquez, were “leaders whose constituents trust them, respect them, and they move votes.”

“To have Hakeem Jeffries standing up with me saying, ‘This is my candidate,’ is hugely impactful in a critically important part of this city to win for anyone who wants to be mayor of New York City,” she added.

In the June primary, New Yorkers will be able to rank up to five mayoral candidates, and Mr. Jeffries indicated that he might reveal other rankings of his choices for mayor but said he had not yet reached a decision on how he would proceed.

On Sunday, Michael Vachon, a spokesman for the billionaire philanthropist and liberal megadonor George Soros, indicated that Mr. Soros would be giving $500,000 to a pro-Wiley initiative, citing the endorsement from Mr. Jeffries. The money is going to an outside spending campaign affiliated with Local 1199 of the Service Employees International Union, the major union supporting Ms. Wiley.

“In light of her commanding performance in the debate and Congressman Jeffries’ endorsement, we have decided to join with 1199 to make sure Maya’s message for N.Y.C. isn’t drowned out by the super PACs supporting men in this campaign,” Mr. Vachon said.

Ms. Wiley once worked at Mr. Soros’s charitable foundation.

The political arm of 1199 will also be investing $500,000 with the hope to raise more, said Gabby Seay, the treasurer of the independent expenditure effort and the political director of the union.

In the interview, Mr. Jeffries sketched out a detailed map of what he saw as Ms. Wiley’s path to victory, though certainly, with a crowded field of candidates, there is significant competition for every major political constituency in New York.