Competence is captivating. No need to tell viewers tuning in to Gov. Andrew M. Cuomo’s daily media briefings. Many have been riveted by his plain talk in the face of a global pandemic.

Others are increasingly focused on the woman usually seated at his left: the one who on a recent Thursday countered a reporter’s suggestion that New York had dragged its heels in response to the spread of the coronavirus by assuring him in a tone like flint that once it was clear that New York, and not just the West Coast, was an entry point for the virus, “we shut down fully, with literally zero guidance from the federal government.”

She is Melissa DeRosa, the trusted aide and strategist to whom Mr. Cuomo routinely turns for a reliable litany of figures and facts: often seen taking notes, checking her cellphone and sliding relevant documents under the nose of her boss. A steady presence on the dais, Ms. DeRosa, 37, is having an extended breakout moment.

As secretary to the governor, she is the most powerful appointed official in the state, the first woman to hold that position, and one of the youngest, her robust command of facts and arcana only hinting at her sway.

“If you’re an Albany lawmaker and you get a call from Melissa DeRosa, you’re essentially getting a call from the governor,” said Lis Smith, the former spokeswoman for Mr. Cuomo’s re-election campaign and the senior communications adviser to Pete Buttigieg during his presidential run.

“In the midst of this crisis, she’s managed to carve out her own role,” Ms. Smith said. A tactician to the bone, “she brings to these briefings her own authoritative voice.”

Ms. DeRosa was certainly tactical in a telephone interview in late April, rarely veering off topic as she cataloged the details of her job. She prepares each day to address a welter of issues.

“Some days it’s, ‘Are we closing schools?’” she said. “Some days it’s, ‘Do we do an executive order to allow people to get married online?’ Some days it’s working with the Bloomberg team to come up with a contact tracing program.”

Armed with charts and documents, she has managed state decisions about voting by mail and restaurant closures, and each day sets the agenda behind Mr. Cuomo’s public messaging.

“It’s not easy to match his confidence, his sense of control during those briefings, but she does,” Ms. Smith said. “She is by no means a ‘yes’ woman. And, as you may imagine, he does not relish hearing no. But he trusts her and values the fact that she’s a straight shooter.”

Mr. Cuomo was quick to echo that appraisal. “This crisis bore down on New York with a force unlike anything we’ve ever seen,” he wrote in an email. “Our response requires an equal and opposite force and that is exactly what Melissa delivers.”

Early Riser

Disciplined as a drill sergeant, Ms. DeRosa is generally up between 3:45 and 4:30 a.m., often in the office by 6, her days sometimes running until midnight. “The governor, when he walks through the door, expects us to be ready with ideas for what we need to be saying to the public for a day, a full briefing,” she said.

“He interrogates us,” she said. “When we tell him something, he doesn’t take it at face value. He’ll ask us a question seven different ways and you’d better be prepared to answer it.”

Afterward, “you spend the rest of the day on the unknown. You can wake up and think that your day is going to go one way, and that plan is out the window by 7:30 a.m. depending on whatever unforeseen crisis happens, whatever the president says, whatever hospital shortage is happening.”

She leaves few details unattended and almost nothing to chance, blitzing her team of 79 state commissioners and all senior staff members each morning with questions. “I ask, ‘Where in the law does it say that you can’t just do voting by mail and you have to do absentee? I want you to recite to me the section of the state constitution. I want to see where it’s written.’”

“I want to make sure that what we’re saying is correct and holds up to public scrutiny,” Ms. DeRosa said.

The task requires agility, and an adamantine core. Ms. DeRosa is known to be unyielding in her support of the governor. “She and I had one disagreement, as much my fault as hers,” recalled Karen Hinton, a communications consultant, who, as press secretary to New York Mayor Bill de Blasio in 2015 and 2016, dealt with Ms. DeRosa.

“Melissa is incredibly smart, very knowledgeable and articulate, and sometimes people can be intimidated by that,” Ms. Hinton said.

“Politics can be tough,” she added. “You have to lay out your views and your positions. Melissa is good at doing that.”

Some qualities, friends suggest, are in her DNA.

“Melissa was always pretty competitive, she always commanded the room,” said Rachel Berman, a dietitian and close friend of Ms. DeRosa’s since the two attended Camp Wah-Nee in Connecticut when they were 12. “From a young age she knew what she wanted to do with her life. She wanted to be in public service. She was very driven, in a professional way.”

Her agenda has been advanced, and impeded, at times, by her family connections. Her father, Giorgio DeRosa, is a partner at Bolton-St. Johns, a highly influential lobbying firm. Her sister Jessica and brother Joseph also work at the firm.

Her husband, Matt Wing, was a Cuomo press secretary in 2013 and 2014, and went on to become the communications director for the governor’s re-election campaign. The couple met in 2013 when Ms. DeRosa was Governor Cuomo’s communications director. In 2015, Mr. Wing became a senior communications officer at Uber as the company sought expansion in New York.

Ms. DeRosa’s appointment in 2017 to the top post in Mr. Cuomo’s office has raised questions about potential conflicts arising from her father’s lobbying. Common Cause, an advocacy group for good government, released a statement at the time, advising that Ms. DeRosa recuse herself from any issue involving her father or family.

No conflicts have been made public since her appointment. But Susan Lerner, the executive director of Common Cause/NY, wrote in an email: “As the governor further consolidates power in this crisis, Common Cause/NY’s concerns about staff conflicts of interest have only intensified. Who is meeting with whom? Who’s getting contracts and who’s not?”

Ms. DeRosa dismissed such unease.

“I don’t get to decide for family what their jobs are, and they don’t get to decide for me what my job is,” she said, adding tersely, “I do my best to live up to the highest ethical standards and be transparent as possible, and I think that is all you can ask.”

‘He Looks to Her’

At 16, Ms. DeRosa began working as an intern for the political director of the New York State A.F.L.-C.I.O., which was preparing to endorse Hillary Clinton ahead of her bid for the Senate.

“I remember thinking while I was doing the envelope stuffing and answering the phone,” she told The Poughkeepsie Journal, “that someday I want to be the person who’s sitting in that room and driving those conversations and mapping out strategies, and being a part of it in a meaningful way.”

There were a few detours. After graduating from the School of Industrial and Labor Relations at Cornell University, Ms. DeRosa became a publicist for Theory, a fashion house in New York, for a year, a stint she now characterizes as a brief rebellious phase.

“I think every 22-year-old tries to keep their father on their toes,” she said with a laugh. “That’s what I was doing at the time.”

She joined Bolton-St. Johns as a lobbyist, pursued a master’s degree from Cornell in public administration and went on to lead former President Barack Obama’s national political action organization for New York. She spent another two years as the deputy chief of staff to the state attorney general Eric Schneiderman, but knew nothing at the time, she said, of the allegations of sexual misconduct that would force him out of office.

Ms. DeRosa is herself no stranger to sexism. She told The Poughkeepsie Journal that as far back as a decade ago, when she was working as a lobbyist, she overheard her boss tell a client, whom she described as a national figure in progressive politics, that she would take the lead on a project. “Why doesn’t she take the lead right up to my hotel room,” came his reply.

The memory still rankles. “All that I have ever wanted is to be seen for and judged on my own accomplishments and competence and merits,” she said.

She joined the New York state administration in 2013 as communications director, and was promoted two years later to chief of staff. She has long had the governor’s ear, Ms. Smith said: “When they’re in a room together, he looks to her to see how she reacts.”

Ms. DeRosa has, with Governor Cuomo’s blessing, helped steer statewide policies including the $15 minimum wage, paid family leave and expanded insurance coverage for in vitro fertilization and egg freezing.

As chair of the New York State Council on Women and newly appointed head of the Covid-19 maternity task force, she was instrumental in pushing through a bill to admit support people to the delivery room, expand birthing options and extend the period of time a healthy partner could remain with a mother after delivery.

Women’s reproductive issues are close to her heart. After six months in her current job, one she knew would consume her waking hours, Ms. DeRosa talked with her doctor about freezing her eggs. “Being a woman in her mid-30s who’s dealing with decisions around having children, when to have children and the limitations in the insurance law and health care, that was something I was very, very involved in,” she said.

Intent on taking charge of her own reproductive future, she underwent the procedure, “through many cycles,” she said. “I’ve done lots of months of hormone shots.”

She is more lax about routine self-care, her days fueled by an old-fashioned elixir. “It’s incredible,” she said, “what the combination of adrenaline and caffeine can do to push you through anything.”

A wearying schedule hasn’t dampened her longstanding interest in the realm of style. She was a determinedly girly girl, her friend Ms. Berman recalled. “Growing up, everything in the closet was a shade of pink, with pearls,” she said.

Two years ago, Ms. DeRosa appeared on a billboard in Times Square wearing a $228 Rebecca Minkoff dress, part of Ms. Minkoff’s advertising campaign. Jezebel, the feminist website, was swift to weigh in with an article carrying the headline “When Public Official Sells Feminism, Who Is Being Empowered?” The article chided Ms. DeRosa for her role in commercializing women’s activism and questioned the ethics of that choice.

Ms. DeRosa has since grown more worldly, if not necessarily more circumspect. She drew feminist ire when, during Cynthia Nixon’s run for New York governor in 2018, she called Ms. Nixon “unhinged,” on her Twitter account.

Viewers often remark on her trademark sleeveless dresses. Is she aiming to bring a dose of glamour to the job? Not a chance, Ms. DeRosa said: “I am in Albany with the clothes that I showed up with. I didn’t set out in this thinking that we were going to be on nationally televised press conferences every single day.”

She has put personal vanity on hold, she said. “I would love to tell you that I do get to go for long runs and have me time and have some semblance of work-life balance, but, I don’t,” she said. “And I think right now that’s the way it’s supposed to be.”