WASHINGTON — When Alabama’s Shelby County sued nearly a decade ago to strike down key pieces of the Voting Rights Act, a civil rights lawyer named Kristen Clarke helped to argue that the entire law should be upheld. A district court agreed, reaffirming that local governments with a history of discriminatory voting practices needed federal permission to change their voting laws.

Though the Supreme Court ultimately overturned the lower-court ruling, the case helped establish Ms. Clarke as one of the nation’s foremost advocates for voting rights protections. Nominated by President Biden to lead the Justice Department’s Civil Rights Division, she would if confirmed be likely to play a key role on the issue for the administration, which has made defense of voting rights a priority as states including Georgia work to enact laws that restrict access to the ballot box.

Mr. Biden called Georgia’s recently passed legislation “Jim Crow in the 21st century,” and he and Attorney General Merrick B. Garland have said that the government must preserve the right to vote.

“I will follow their lead in ensuring that the Civil Rights Division, if I am confirmed, is using the tools in its arsenal — the Voting Rights Act, the National Voter Registration Act, the Uniformed and Overseas Absentee Citizens Voting Act — to ensure that eligible Americans have access to the ballot in our country,” Ms. Clarke said on Wednesday during her confirmation hearing before the Senate Judiciary Committee.

Ms. Clarke, 46, who would be the first Senate-confirmed leader of the Civil Rights Division to be a woman of color, testified alongside Todd Kim, a Justice Department veteran and Mr. Biden’s choice to run its Environmental and Natural Resources Division. Mr. Kim told senators that protecting the nation’s “shared interest in the environment and our natural resources” was a calling.

Several civil rights issues, including the uptick in violence against Asian-Americans and high-profile police killings of Black people, have made civil rights enforcement one of Mr. Biden’s most visible agenda items.

Mr. Garland has asked for a 30-day expedited review to determine how the department can most effectively use its resources to combat hate crimes, and he told civil rights leaders on Wednesday that the department would scrutinize whether government agencies, including police departments, engaged in “patterns or practices that deprive individuals of their federal or constitutional rights.”

Mr. Garland also called the Civil Rights Division “the tip of the spear of the Justice Department’s effort to ensure justice for all.”

He said that Ms. Clarke’s skills and experiences would help the department successfully combat discrimination “in areas from housing to education to employment” and “ensure accountability for law enforcement misconduct.”

Democrats on the Judiciary Committee indicated that they viewed Ms. Clarke’s voting rights work as one of her strongest qualifications to restore a division that they argued had been crippled by the Trump administration.

“Under Trump, the Civil Rights Division reversed longstanding positions in key voting rights cases, giving its blessing to harmful voter ID laws and voter purges,” Senator Richard J. Durbin, Democrat of Illinois and the chairman of the committee, said in his opening remarks.

“Ms. Clarke,” he added, “has tirelessly pursued an objective that sadly remains elusive even today — equal justice for all.”

Republicans on the committee accused Ms. Clarke of being anti-police, an allegation she denied. Police groups including the Major Cities Chiefs Association and the head of the International Association of Chiefs of Police have backed her confirmation.

Republican senators asked whether Ms. Clarke supported defunding the police, a slogan and mission embraced by many on the progressive left to cut police budgets or even abolish police departments altogether. The movement has been rejected by policing groups, Republicans and many moderate Democrats, including Mr. Biden and Mr. Garland.

Senator Ted Cruz, Republican of Texas, homed in on an op-ed that Ms. Clarke wrote last June for Newsweek: “I Prosecuted Police Killings. Defund the Police — but Be Strategic.”

“You just said you don’t support cutting funds from police. I find that astonishing,” Mr. Cruz said. “In three paragraphs in your article you begin with the words, ‘We must invest less in police.’”

Ms. Clarke insisted that she did not support defunding the police.

“I wrote that op-ed without having the power of the purse string behind me and talked about how we can allocate a limited pool of resources in a more effective way,” she told Mr. Cruz. “President Biden is committing more resources to police, and I think that’s a great thing.”

The daughter of Jamaican immigrants who raised her in a Brooklyn housing project, Ms. Clarke attended the prestigious Choate Rosemary Hall in Connecticut through Prep for Prep, a program that helps students from modest backgrounds attend top private schools. She went on to study at Harvard and Columbia Law School.

Ms. Clarke said that a class trip to Hartford, Conn., to hear arguments in Sheff v. O’Neill, which went on to become a landmark school desegregation case, inspired her to be a civil rights lawyer.

“That moment was a powerful display of the role civil rights lawyers play in our society,” she told the committee. “I was mesmerized and deeply moved as I watched attorneys argue for more just and equitable educational opportunities.”

She rejected a corporate law job to join the Justice Department, working in the Civil Rights Division during the George W. Bush administration. She worked at the voting rights project at the NAACP Legal Defense and Educational Fund, and at the Civil Rights Bureau in the New York attorney general’s office, where she led an initiative to protect the right of Jewish employees to observe the Sabbath and religious holidays.

In 2015, Ms. Clarke became the leader of the Lawyers’ Committee for Civil Rights Under Law, an organization formed during the civil rights movement.

While Republicans expressed skepticism of Ms. Clarke, they directed few questions toward Mr. Kim, who has spent much of his career as a government lawyer enforcing the nation’s environmental laws.

The son of Korean immigrants, Mr. Kim joined the Justice Department through its Honors Program, as did Ms. Clarke. He spent seven and a half years in the environmental division before serving as the District of Columbia’s first solicitor general.

While a lawyer in the Justice Department’s environmental division, Mr. Kim said, he worked on cases involving the Clean Water Act, the Clean Air Act, Superfund site cleanups and Native American land rights. Mr. Biden has said that he will prioritize environmental conservation, and has signed executive orders aimed at strengthening environmental protections.