In a lace-accented white wedding gown, Chirlane McCray, the first lady of New York City, made her way up the church aisle and turned to face the crowd. Arrayed before her were not the familiar faces of friends and family, but dozens of other women in similar bridal attire as they prepared to march across Upper Manhattan in solidarity against domestic violence.

“There’s nothing like putting on the garb,” she said after the event last month.

After nearly one full term, Ms. McCray, the wife of Mayor Bill de Blasio, has fully wrapped herself in the role of political spouse, a job especially steeped with symbolism for her. As the African-American wife of a white mayor in a moment of renewed racial strife across America, Ms. McCray has emerged as likely the most influential, if not consequential, first lady in the city’s history.

She has a full-time staff of five and her own public schedule. She oversees a portfolio of municipal programs, including her signature $850 million mental health initiative, in which other city officials report to her. She controls an independent nonprofit with a $25 million annual budget and still more staff. And she has the mayor’s ear on decisions big and small, sitting in on top-level job interviews, policy formulation and senior staff meetings.

“Where’s Chirlane?” is a regular refrain heard around City Hall as Mr. de Blasio wonders aloud why she is not in a particular meeting, or where she stands on an issue.

