The father got a big new job, only to face a seemingly agonizing choice: Should he stay in the house he owned in the neighborhood he said he loved, or move to the much fancier house that came with the job?

Mayor-elect Bill de Blasio declared his intention on Wednesday, bidding farewell to his rowhouse in Park Slope, Brooklyn, and saying he was bound for Gracie Mansion, on the Upper East Side of Manhattan. The word came in a letter titled “Family Decision” that was posted on Mr. de Blasio’s website and signed by all four de Blasios — the mayor-elect; his wife, Chirlane McCray; their college-age daughter, Chiara, and their teenage son, Dante.

His family’s decision will make Mr. de Blasio, a Democrat, the first mayor to live in Gracie Mansion since Mayor Rudolph W. Giuliani and the first since the Sept. 11 attacks. By then, Mr. Giuliani’s marriage to Donna Hanover had disintegrated, and he had moved out. His successor, Mayor Michael R. Bloomberg, poured millions into renovations at Gracie Mansion without spending a single night there. Home remained his townhouse a mile and a half away.

For Mr. de Blasio, the decision was not just about a move from ZIP code 11215 in Park Slope to 10128 on the Upper East Side. It was about how that move would be perceived by the voters who elected him, after a campaign that channeled resentment against high-visibility wealth and the inequalities it has created — and, in particular, the disparities between Manhattan and the other boroughs.