Consultants at McKinsey & Co. often joke that they can double their salaries and cut their hours in half when they leave the firm for another private sector job. When Rohit Aggarwala left McKinsey last summer to head a new New York City agency, the Office of Long-Term Planning and Sustainability, he failed on both counts.

Mr. Aggarwala, 35, is the slim, soft-spoken technocrat who has spent the last year crafting PlaNYC, Mayor Bloomberg’s 127-point roadmap for New York City to prepare for an expected influx of 1 million new residents by 2030. The plan includes a new tax on traffic in Manhattan and an effort to plant 1 million new trees in the city.

Mr. Aggarwala has a professorial air that befits someone who has earned four degrees from Columbia University, including a doctorate in history and an MBA. He has handed out more than 3,000 business cards over the past year. A mass transit devotee, he does not own a car and rides the E train to work at City Hall every day from his home in Hell’s Kitchen. While he theoretically enjoys cooking, he acknowledges that his refrigerator has stood empty over the past 12 months while he has devoted himself to PlaNYC.

“My most typical lunch has been nothing,” Mr. Aggarwala said in an interview at his office on Broadway, across the street from City Hall. Dinner often came delivered to City Hall in pizza boxes or in cartons from Zen Palate, and it has been months, he said, since his Blackberry was turned off or placed out of his reach.

If Mayor Bloomberg and Deputy Mayor Daniel Doctoroff have been at the center of the effort to explain PlaNYC to the public and get it passed in Albany, Mr. Aggarwala has been a crucial player behind the scenes, gathering input and building early support for the plan from business and civic leaders, community groups, elected officials, academic experts, and thousands of New Yorkers across the city.

Mr. Aggarwala, known to friends and colleagues as “Rit,” grew up in the Westchester County New York suburb of White Plains, and moved to Rome, Italy during high school when his father, an Indian project manager for the United Nations, was transferred there on assignment. His mother, an Irish-American from Queens, works as a teacher, and his brother as an aero-space engineer.

While he still spends his free time writing chapters of a book he plans to publish about how New York City surpassed Philadelphia as an economic hub in the 1800s, Mr. Aggarwala for now has strayed far from academia.

Mr. Aggarwala was serving a McKinsey client in the suburbs of New York when he was approached by Marc Ricks, a senior policy adviser to Mr. Doctoroff, who asked him to present his ideas on transportation to Mr. Doctoroff.

“Marc said ‘do you consider yourself a transportation advocate?’ He said ‘for the price of a resume, you get to tell the deputy mayor what you think about transportation,'” Mr. Aggarwala recalled. When Mr. Aggarwala began to understand the “bigness” of the mayor’s vision for creating a sustainable New York City, the job offer that followed his presentation to Mr. Doctoroff was one he said he felt he couldn’t refuse.

“I’ve been a committed Democrat all my life, but a fan of the mayor’s since the beginning for his willingness to face facts,” Mr. Aggarwala said. He said he would consider working for Mr. Bloomberg on a presidential run if the mayor asked for his help. “He could do anything he wanted,” he said when asked about Mr. Bloomberg’s presidential aspirations.

Over the past year, Mr. Aggarwala said, there was no typical day at work. He was often the first to arrive at his office around 7:30 a.m, and returned home to his apartment late in the night after talking to New Yorkers at town hall meetings about their ideas for creating a greater, greener, New York City.

“We’d have meetings at 7 or 8 in the evening, but there were always people who wanted to linger and talk, which was great,” he said.

Mr. Aggarwala seems more accustomed to working behind the scenes analyzing data. He has earned a reputation for being more modest, if less charismatic, than his boss, Mr. Doctoroff.

“What are we here to talk about?” he asked this reporter, and seemed mildly embarrassed when reminded that the subject of the interview was him.

“Dan Doctoroff likes very smart people who can be jacks of all trades,” the president and CEO of the Partnership for New York City who served on the PlaNYC advisory board, Kathryn Wylde, said. “Rit is the kind of person you would want to implement your vision and to frame it and build consensus around it.”

The two personalities — the visionary and the implementer — complemented each other well in assembling an operational plan for New York City, according to members of the advisory board that worked alongside them.

At a briefing for reporters on the Saturday before Mr. Bloomberg unveiled PlaNYC in front of an energized crowd of 700 supporters at the Museum of Natural History, Mr. Aggarwala gave the presentation a test run of sorts in front of a handful of reporters in City Hall’s Blue Room. As he rattled off details about cleaning up brownfields, establishing a transit financing authority, and strengthening energy codes in New York City, Mr. Doctoroff had to signal to him from the back of the room that he was getting bogged down in too many details, that he had to move the presentation along.

Where Mr. Doctoroff seems adept at boiling down an exhaustive plan into a rousing message, Mr. Aggarwala’s presentation at times seemed merely exhaustive.

It is Mr. Aggarwala’s intimate knowledge of the data culled from thousands of conversations with New Yorkers, however, that city leaders say give the plan a greater chance of success than Mr. Doctoroff’s previous oversized dreams for New York City — the 2012 Olympics bid and his plan to build a stadium for the Jets on Manhattan’s West Side — that ultimately failed to win state support.

“Compare this with the Olympics bid, and they’ve done things the opposite way,” a Columbia University professor who served on the advisory board, Esther Fuchs, said in an interview.

“It wasn’t so much me and Dan surveying the city in some omniscient way, saying ‘this is what we need,'” Mr. Aggarwala said. “We met with a lot of people.”

The bullpen at City Hall has a clock counting down the number of days the Bloomberg administration has left in office (947). The limited time the mayor has left in office makes it more desirable to build coalitions that can support big plans under future mayors.

“The commitment to outreach, listen, and build a broad coalition was probably influenced by the lessons of the stadium,” Mr. Aggarwala said. “It made the plan better.”

Since the plan was announced earlier this year, Mr. Aggarwala and his staff of 10 have met with more than 100 advocacy organizations and sifted through more than 3,000 e-mails received through its Web site.

“He ran with the mayor’s concept and came up with an operational plan,” Ms. Fuchs said.

Mr. Aggarwala, a facilitator by training and a transportation wonk by nature, worked in the U.S. Department of Transportation in the Clinton administration before joining McKinsey, and served a brief stint in Albany as a transportation policy advisor to Assemblyman Samuel Hoyt, a Democrat of Buffalo. “We shared a passion for high-speed trains,” Mr. Hoyt said in an interview. “My memory of Rit is that he would get passionate about something and put in endless hours to make it happen. In one legislative session, he made more progress on the issue of high-speed rail in the region than we ever had before.”

Mr. Aggarwala’s practical solutions to Mr. Bloomberg’s lofty goals have not pleased everyone. “A 10-minute walk to a park could include public space that’s made park-like,” such as Herald Square or Times Square, Mr. Aggarwala said earlier this year at a Forum for Urban Design conference. Some environmentalists at the speech balked at what they said was an overly-broad definition of park space, and a dodge for achieving the goal of having every New Yorker reside within a 10-minute walk of a park.

The proposal to charge drivers a fee to use Manhattan’s most crowded streets during rush hour quickly emerged as the most political contentious initiative in the plan. “Congestion pricing was London’s smoking ban,” Mr. Aggarwala said. “They did it first and many cities around the world are now thinking it can work.”

The idea of instituting congestion pricing on the streets of Manhattan was on the table very early in the planning process, Mr. Aggarwala said. “I don’t think anyone’s going to come up with a plan without congestion pricing,” he said. “We tried and we couldn’t. Other initiatives are already in the plan and they’re not enough to close the $31 billion transportation funding gap this region faces.”

The Office of Long Term Planning and Sustainability will likely become a permanent office at City Hall, Mr. Aggarwala said. While his working in crafting the plan is done, he said the hardest part of his job may lie ahead. “Now we have 127 initiatives to implement,” he said. “When it identifies the lead agency, it often says us.”