The two met for a little over an hour at Trump Tower in Manhattan.
De Blasio called the meeting "respectful" and "candid" with a real "give-and-take."
The mayor, a liberal Democrat, and Trump have previously clashed. He cited concerns with Trump's support of aggressive policing tactics, his tax plans and any move to deport immigrants living in the United States illegally.
"I talked to him about concerns about proposed deportations," said de Blasio. "I gave him the perspective of the NYPD that any initiative that would create a rift between our police all over the country and the communities they serve that would make it impossible for police and community to communicate that would show distrust between law enforcement and neighborhoods would be counterproductive."
De Blasio said that Trump "loves this city" and added that he urged the Republican president-elect to send a "sign of unity" to his hometown, which overwhelmingly voted for Democrat Hillary Clinton.
The mayor held a press conference afterwards outside Trump Tower:
As he entered the tower around 10:50 a.m., reporters asked him about the meeting.
"We're talking about what the people of New York City are feeling and what we need," de Blasio said.
De Blasio, who boarded the elevators very quickly, did not respond to a question about whether he is concerned about a spike in hate crimes in the city.
(The Associated Press contributed to this report.)