“Reform is just a must at this point,” Mr. Heastie said.

Carl Edward Heastie was born on Sept. 25, 1967, in the Bronx. His mother was a nurse, and his father worked various jobs, including as a dental technician and a cabdriver. In elementary school, Mr. Heastie recalled, he twice ran for class president “and got creamed both times.”

He graduated from Stony Brook University with a degree in applied mathematics and statistics. He also served in student government, which he described as a formative experience. He said he was still paying off his student loans.

A few years after college, Mr. Heastie took a job at the New York City comptroller’s office, where he joined a group of budget analysts who were a bit older and had been working together for some time. He fit in right away, writing sections of reports that analyzed the city’s finances, his boss at the time, Richard Halverson, said.

“He was definitely going somewhere,” Mr. Halverson said, and was “very serious about government” — not the kind of person, he added, who planned to put in a few years and then become a banker.

Mr. Heastie was also immersing himself in Bronx politics. He served in the 1990s as a campaign treasurer for Larry B. Seabrook, who in a long career served in the Assembly and the Senate, and on the City Council. (Mr. Seabrook is now in prison, convicted in 2012 of funneling city money to his relatives and girlfriend.)

In 1997, Mr. Heastie’s mother, Helene Heastie, and a colleague were charged with stealing more than $197,000 from a publicly funded social services agency where they worked; she pleaded guilty to grand larceny the next year and died not long after.