He explained in subdued tones that his arrest after an Oct. 31, 2012, traffic stop on suspicion of marijuana possession cost him money, tarnished his reputation at a key point in his career, and dredged up old memories of a rough childhood in North Philadelphia.
"In neighborhoods like where I come from, four black males in a car . . . we're always being asked to be searched," he said. "All I was doing that night was going to work and doing what I had to do."
In a lawsuit filed against the city last year, Williams contended that two of the officers who stopped him that night - Andre Boyer and Alvin Outlaw - fabricated a reason to detain him.
No marijuana was found in his car. Williams was never charged. And while he was held at the 22d District for more than eight hours, other officers shot cellphone photos of him that spread quickly over the Internet.
"Talk about Dreams and Nightmares," Officer Victoria Ayres wrote, using a reference to Mills' first album in her Instagram post from that night.
"Meek is sitting in cuffs courtesy of the 22nd District!" she continued. "I'm rollin! Maybe he'll sign our copies!"
The delay caused Williams to miss a scheduled appearance in Atlanta that evening worth $39,000. The publicity surrounding his run-in with police cost him endorsement deals including a potential $1.3 million raise on a contract with athletic wear brand Puma, his lawyer, Dennis Cogan, said.
Later, that run-in led to Williams' conviction on a violation of probation for prior drug and gun convictions and an order from a Philadelphia judge that he not leave the city months after his debut album was released at No. 2 on the Billboard charts.
"I kept thinking, I'm on probation, I'm going to jail," Williams testified Monday. "Everything I worked for in the last 10 years - it could all be over in a day."
But city attorneys representing Boyer and Outlaw maintained that the officers were just following standard procedure.
They stopped Williams' Range Rover after noticing an unusually dark tint on the windows.
They smelled marijuana, called in a narcotics dog that also reacted to the car, and eventually brought Williams and his entourage - a group that included a cousin, an off-duty Florida narcotics officer, and a senior vice president at Warner Bros. music - into the station until they could conduct a full search of the vehicle.
The fact that drugs were never found doesn't invalidate the officers' reasons to be suspicious, said city lawyer Armando Brigandi.
"An inconvenience? Absolutely," he said. "But not every investigation turns out to result in criminal charges."
Cogan is expected to make much of previous complaints against Boyer as the trial continues this week.
A 17-year veteran of the force, Boyer was fired last year after the Police Board of Inquiry cited him for a handful of violations over the seizure of $6,000 in cash from a suspect during a 2011 arrest.
At the time, he was also the target of more citizen complaints than any other officer on the force, including several involving incidents in which he said he smelled marijuana as a reason to stop or detain suspects.
"That man should never have been on the street that day he came into contact with Meek Mill," Cogan told the jury.
Throughout Monday's proceedings, U.S. Magistrate Judge Timothy Rice appeared unfazed by the celebrity in his courtroom - unlike a crowd of backpack-toting students from Constitution High School who filled the courtroom on a class trip.
More than a few said they hoped to snag an autograph.