Yusef Salaam stood at the front of the City Council Chamber in Lower Manhattan with his right hand raised and his left hand on the Quran held by his wife. It was the one that his mother gave him when he was 15 years old and standing trial for a crime he did not commit. Its pages, filled with notes and bookmarks, were kept intact by a cloth cover that Mr. Salaam made during nearly seven years in prison.

Surrounded by relatives including his mother, sister and some of his children, Mr. Salaam was asked by Michael McSweeney, the city clerk, to repeat an oath.

With each passage that Mr. McSweeney recited and Mr. Salaam repeated, their voices took on volume and urgency: “I will support the Constitution of the United States and the Constitution of the State of New York,” Mr. Salaam said. “I will faithfully discharge the duties of the office of council member of the ninth district, in the borough and county of New York, in the City of New York, according to the best of my ability.”

“Council Member Salaam,” Mr. McSweeney said, “Congratulations.”

Mr. Salaam’s family broke into cheers. He placed his hand over his heart.

It was one day and 21 years after his exoneration from a first-degree rape conviction in a case so brutal that it had stunned a crime-weary city and aligned New York’s political, law enforcement and media establishment squarely against him and his co-defendants.