On the day Judge Tanya S. Chutkan was randomly selected to preside over former President Donald J. Trump’s trial on charges of conspiring to overturn the 2020 election, she called a childhood friend in Jamaica, Christine Stiebel. Judge Chutkan, who is not especially religious, said to her friend, as Ms. Stiebel recalled it: “Chris, please pray for me. I’ve got the case.”

It was a rare display of unease, even in private, for a woman who has cultivated a seven-year reputation as a temperate but unflinching jurist. Judge Chutkan, 61, a former public defender and civil litigator, will be overseeing the first federal trial of Mr. Trump, set to begin on March 4. The spectacle conjures up the possibility of a likely Republican presidential nominee facing conviction and potential prison time for an assault on American democracy, all before voters go to the polls next November.

Mr. Trump has already attacked Judge Chutkan as “VERY BIASED & UNFAIR” on social media. His attorneys have argued that the judge, an Obama appointee, should recuse herself because they believe her statements in other cases related to the Jan. 6 attack on the Capitol show a bias against their client. Prosecutors have in turn asked Judge Chutkan to place a limited gag order on the former president, citing his “near-daily” social media attacks on people involved in the case.

Judge Chutkan has refused to recuse herself, but a hearing on the gag order will be held on Monday. Judge Chutkan warned in a preliminary hearing that Mr. Trump, who is already under a gag order in a business fraud case in New York, does not have an absolute right to free speech and “must yield to the orderly administration of justice.”

It has not been lost on Mr. Trump that Judge Chutkan, a Black woman who has a history of supporting Democrats, is the antithesis of a Mar-a-Lago habitué. Less known is her commanding presence in the courtroom, a reflection of her extensive trial experience and an upbringing in a prominent Jamaican family. Unfamiliar to the spotlight though she may be, Judge Chutkan has shown little sign of being intimidated by it.

So far she has treated Mr. Trump like any other defendant, and has indicated to colleagues that she will approach the trial as she would any criminal proceeding. Even in the midst of a history-making case against a former president, she continues to take on more routine cases and has not requested a reduction in her docket.

But there are differences. Because of threats to her life from Trump supporters, Judge Chutkan no longer rides the five miles by bicycle from her house to the federal courthouse in Washington. Instead she jogs with U.S. marshals on different routes, and then they drive her to work.

On a recent Tuesday morning, she entered the courthouse smiling broadly in Lycra shorts and tennis shoes, flanked by federal marshals and toting a water bottle. When someone in the hallway said that she made for an exuberant sight among all the dark-suited attorneys, the judge chortled, “Perhaps irrational exuberance,” and continued her swift pace to her chambers.

“One trait of my sister’s that makes her good at her job is that she’s not terribly concerned with other people’s opinions of her,” said her younger sister, Robynne Chutkan, a gastroenterologist and author.

On the bench, Judge Chutkan is given equally to bouts of tartness and courtroom banter. When one of Mr. Trump’s attorneys, John F. Lauro, responded to a remark of hers by saying that she had “hit the nail on the head,” Judge Chutkan archly replied, “That may be the last time you say this for a while.”

Judge Chutkan, second from right, in 1977.Credit…via Robynne Chutkan

Judge Chutkan is one of the few district court judges in the country to come from the ranks of public defenders, which has informed her rulings. Last month, she granted an emergency motion to release a convicted robber from custody so that he could attend his brother’s funeral a few miles away in Maryland. And she frequently cites her own experiences as a defense attorney pitted against federal prosecutors with seemingly infinite resources.

When Mr. Lauro complained in a hearing in the Trump case in August that the government “has been searching for prior orders in cases that I had no idea about,” Judge Chutkan responded reassuringly, “I hear you. I feel your pain.”

Heather Shaner, a Washington defense lawyer who has argued cases before Judge Chutkan, said of her, “What stands out, besides her intelligence and fairness, is that she’s very cognizant of the fact that defendants aren’t lawyers — she’s always very clear in her rulings.”

But Judge Chutkan has been conspicuously less charitable when it comes to the several Jan. 6 defendants who have been tried in her courtroom. In numerous cases she has brushed aside the government’s recommendation of probation or home detention and has instead ordered jail time for those who entered the Capitol that day.

“There have to be consequences for participating in an attempted violent overthrow of the government, beyond sitting at home,” she declared while issuing a 45-day prison sentence to a defendant in October 2021.

“For someone who is not very sentimental, my sister is surprisingly patriotic,” Robynne Chutkan said. “We come from a country that has a more precarious relationship with democracy than America. It gives her a reverence for democratic institutions, whether it’s the orderly transfer of power or everyone being deserving of a fair defense.”

Tanya Chutkan did not lack for role models.

Her paternal great-grandparents were indentured servants brought from India by British planters to toil on Jamaican sugar estates. Her father, Winston Chutkan, was born on a plantation. In 1948, he received a scholarship to a prestigious boarding school, Jamaica College, awarded annually to a single young plantation resident.

“I wore shoes and experienced indoor plumbing for the first time in my life,” he said in an interview on Saturday, speaking of his experiences at the school. He went on to become a successful orthopedic surgeon and counted among his patients Bob Marley, the Jamaican reggae legend.

Judge Chutkan’s maternal grandfather, Frank Hill, a newspaper reporter and radio host, was a socialist and an early leader in the People’s National Party who spent more than four months in detainment in 1942 for agitating against repressive conditions in colonial Jamaica. A decade later, he and three others were expelled from the party for what the members said was their communist activity. Mr. Hill later renounced their far-left ideology as a “major mistake” that momentarily weakened the national movement for independence, which came in 1962.

“Socialism is nonsense,” Ms. Chutkan’s grandfather said in a 1978 interview in The Gleaner, Jamaica’s oldest daily newspaper. “What I believe in is Jamaicanism.”

But it was Mr. Hill’s daughter, Noelle Hill Chutkan, who would serve as her daughter Tanya’s lodestar. An English instructor and dancer who became director of the National Dance Theater Company in Jamaica, the elder Ms. Chutkan also represented her country in squash and bridge competitions. In her 50s, she earned a law degree from Emory University in Atlanta, and subsequently practiced law, first in Jamaica and then in Washington.

“Seeing how Noelle Chutkan lived her life, Tanya would grow up believing that you can do it all,” said a childhood friend, Andrea Rattray, now a lawyer in Kingston.

Still, Tanya Chutkan did not seem fated to take the world by storm. Friends recall her as a B student who whiled away her days reading novels and playing the Jamaican card game Kalooki. In her senior class yearbook at St. Andrew High School for Girls she offered a self-effacing description: “Ambition: to become a famous dancer. Destiny: permanent usher of the National Dance Theatre Company.”

An advertisement for George Washington University drew her to the nation’s capital, where for the first time in her life Judge Chutkan was outside the Caribbean, attending classes on a campus that was overwhelmingly white. Her friend Ms. Stiebel followed her there and recalled being asked by a classmate if Jamaicans lived in trees. The two expatriate students worked together serving food in the campus cafeteria.

Judge Chutkan, who declined to be interviewed for this article, majored in economics, but friends say she found it dull. After graduating in 1983, she relocated to New York in hopes of pursuing dance as a profession, but a few months with the Dance Theatre of Harlem appeared to have rid her of any such designs.

She then spent four months volunteering for the doomed 1984 presidential campaign of Walter Mondale, an experience that awakened an interest in government and law. After graduating from the University of Pennsylvania law school in 1987, she joined a Washington firm that specialized in civil litigation.

Her cases involved uninspiring arcana like railroad trackage rights, prompting her to apply four years later for a job as a public defender in Washington. Her clients were now indigent defendants accused of drug dealing and violent felonies, but friends say the work ignited her passions. In 1996, she became the office’s lead attorney for sex offenses, and a year later for homicides.

Judge Chutkan also fell in love with a fellow public defender, Peter Krauthamer. They married and had two children. (The two are now divorced.) By 2002, the demands of parenting and long, intense criminal trials had become difficult to bear. She returned to civil work, this time at the firm of Boies Schiller Flexner.

Judge Chutkan seemed mostly content with her life among fellow Beltway multitaskers, spending her free moments at hot-yoga classes, jogging along the trails of Rock Creek Park or talking back to the op-eds while she read them. (A newspaper devotee who consumes every page, including sports scores and obituaries, Judge Chutkan has impressed her judicial colleagues with her breadth of knowledge, which she describes as “a reservoir of trivia.”)

Still, recalled her 88-year-old aunt, Jeanne Barnes, “she was bored by it all.” In 2013, friends in the legal community encouraged her to apply for a vacant seat on the U.S. District Court in Washington. Judge Chutkan was not a power-alley regular, despite contributing a total of $3,273 to Barack Obama’s presidential campaigns and volunteering for his re-election effort. She nonetheless filled out the application, and on June 4, 2014, was confirmed by the Senate, 95-0.

“I’ve never been so excited to receive a pay cut,” she told her sister.

Judge Chutkan came to her new job with a wealth of trial experience. Her ability to assess witnesses and apply the rules of evidence, in addition to extensive preparation before hearings, helped distinguish her from the start, other judges say.

She has since dealt with several high-profile cases.

In 2017, she presided over the case of a 17-year-old undocumented woman from Central America who discovered she was pregnant after she was detained at the Texas border, but was denied the abortion she requested by the Trump administration’s Office of Refugee Resettlement.

That same year, an American suspected of being an enemy combatant was captured by Syrian forces in Iraq and handed over to the Defense Department, which detained him for months without releasing his identity or giving him access to counsel.

In both cases, Judge Chutkan bristled against the government prosecutors, pronouncing herself “astounded” and “frankly amazed” by their positions. Judge Chutkan ruled that the woman could have an abortion and that the detainee was permitted to receive a visit from the American Civil Liberties Union and retain counsel. He is now living in Bahrain.

Two years later, at the sentencing hearing of Maria Butina, a Russian firearms advocate who had failed to register as a foreign agent while collecting information from American conservative activists, Judge Chutkan’s sympathies swerved back toward the government. Though Ms. Butina had pleaded guilty and had cooperated extensively with the F.B.I., the judge still ordered her to serve an additional nine months in prison.

Judge Chutkan observed that the defendant’s information gathering had taken place “at a time when the Russian government was acting to interfere and affect the United States’ political and electoral process.” Her remark struck some legal observers as gratuitous, given that even government prosecutors had not accused Ms. Butina of directly conspiring with Russia to meddle in the 2016 American election.

The sentiment is nevertheless consistent with what allies of Judge Chutkan describe as her commitment, given Jamaica’s history of political violence and unrest, to protecting America’s democratic institutions. In 2021, when she ruled against Mr. Trump’s assertion of executive privilege in refusing to hand over documents to the House committee investigating the Jan. 6 attack, her language was pointed.

“Presidents are not kings,” she wrote, “and plaintiff is not president.”

As Judge Chutkan prepares for Mr. Trump’s trial, one judicial colleague recalled the day in 2019 when the former president’s last confirmed attorney general, William P. Barr, announced that the federal government would resume executions of death row inmates after a nearly two-decade hiatus.

Judge Chutkan agreed to have all the cases transferred to her jurisdiction.

Over the next year and four months, she blocked what would have been the swift executions of 13 people, instead permitting them to appeal the constitutionality of potentially inhumane lethal injections. As a result, several of the prisoners’ cases remain under judicial review.

Judge Chutkan’s judicial colleague, who declined to speak on the record because of professional constraints, pointed out that the stakes of these cases were literally matters of life and death. “You think the Trump case is high pressure?” the colleague said.