Fani Willis was preparing to start her new role as Fulton County District Attorney in Georgia when Donald Trump made a phone call to a top Republican in the state that would upend her work for the next several years.

On 2 January 2021, the former president phoned Georgia Secretary of State Brad Raffensperger and asked him to “find 11,780 votes”, the number he needed to beat Joe Biden, who had won the state and the 2020 presidential election several weeks before.

Audio from the call was leaked to US media the next day, sparking an outcry on Ms Willis’s first day in office.

“How soon I knew an investigation may be warranted was on day one,” Ms Willis told USA Today in 2022. “The phone call was enough to… cause grave concern.”

Two-and-a-half years later, Ms Willis, 52, has indicated that Mr Trump could soon face criminal charges related to her office’s probe into the call and other efforts to overturn the election result in the state.

She is known by fellow Georgia lawyers and those who have worked with her as a dogged prosecutor capable of securing convictions in high-profile and complex cases.

“She had a reputation of always being prepared,” said Melissa Redmon, who worked in the Fulton County District Attorney’s office at the same time as Ms Willis. “Given the type of cases she prosecuted, that took a tremendous amount of dedication.”

Some of Ms Willis’s most-prominent trials to date include a controversial Atlanta Public Schools scandal involving officials who cheated to improve standardised test scores, and several well-known rappers who were accused of gang crimes.

Mr Trump has called her a “young, ambitious, Radical Left” prosecutor, arguing her investigation into his post-election conduct is a political “witch-hunt”.

In multiple interviews with US media outlets, Ms Willis has insisted her office is following the same procedures it would if anyone had potentially committed a crime in her area.

“The reality is, we have a job, and the job is just to try to find the truth,” she told the New York Times in February. “We’re just going to do that [Trump] case like every other.”

The BBC has reached out to Ms Willis’s office for comment.

Born in Inglewood, California in 1971, Ms Willis was raised primarily by her father, a criminal defence lawyer and member of the Black Panthers, the radical political party which championed black rights.

The district attorney has said her father’s work led her to the courthouse from an early age.

She graduated from the historically black college Howard University in 1993, before receiving a law degree from Emory University in Georgia in 1996.

Just five years later, Ms Willis joined the Fulton County District Attorney’s office, where she served in several different divisions until 2018.

During her nearly two decades there, Ms Willis led more than 100 jury trials, including the longest criminal trial in Georgia history. It ended with convictions for 11 of 12 Atlanta public school officials accused of cheating on state-administered standardised tests in 2009 for better bonuses and promotions.

Her successful trials quickly secured her a reputation of being an exceptionally skilled prosecutor, even among the accused, said Ms Redmon. During her time at the DA’s office, Ms Redmon remembers hearing a defendant once plead with a relative to try to get a witness to leave town because the prosecutor tackling their case, Ms Willis, was “a genius”.

After her time in the office ended, Ms Willis spent several years in private practice. Then, in 2020, she decided to go head-to-head with her former boss, six-term Fulton County District Attorney Paul Howard.

She won in a runoff election with 73% of the votes, becoming the first black woman to serve as Fulton County’s top prosecutor. As Fulton County’s district attorney, she is responsible for representing the government in criminal cases, investigating crimes in the county, determining whether charges should be brought and prosecuting cases in court.

Ms Willis launched the investigation into Mr Trump’s post-election conduct just a month after his infamous phone call to Mr Raffensperger.

Her office has interviewed dozens of witnesses, including top Georgia Republican officials like Governor Brian Kemp and Mr Raffensperger as well as Mr Trump’s former lawyer Rudy Giuliani.

Ms Willis has done so while under attack from Mr Trump, who has taken to his social media platform Truth Social to repeatedly lambast the probe. The “Radical Left Democrat ‘Prosecutor’ from Georgia who is presiding over one of the most Crime Ridden and Corrupt places in the USA, Fulton County, has put together a Grand Jury to investigate an absolutely ‘PERFECT’ phone call to the Secretary of State”, he wrote in 2022.

In response to the former president’s attacks, Ms Willis has argued that no one is above the law.

“I do not have the right to look the other way on a crime that could have impacted a major right of people in this community and throughout the nation,” she told the New York Times last September.

She has faced threatening messages – some littered with racist and sexist language – because of the work, according to emails she reportedly forwarded to Fulton County commissioners.

Ms Willis has faced other criticisms in connection to the Georgia probe. Last year, a judge reprimanded her for hosting a fundraiser for a political opponent of one of the targets of the investigation, Republican state Senator Burt Jones. Mr Jones was one of 11 “fake electors” accused of signing paperwork falsely claiming Mr Trump had won the election.

Fulton County Judge Robert McBurney called her decision to raise funds for Mr Jones’ political rival a “what-are-you-thinking moment” and ruled she could no longer investigate him as a part of the probe.

Those who know Ms Willis and her work, however, argued that she has largely carried out the high-stakes investigation with the same meticulousness that she has demonstrated in previous cases.

“She has handled this [Trump] situation with remarkable professionalism and grace,” said Morgan Cloud, a professor at Emory University School of Law. “She hasn’t rushed it in any way.”

“This is a huge case, so of course it will be a big deal for her if she wins, and a big deal if she loses,” he said.

With additional reporting from Kayla Epstein