The man charged with killing a homeless subway passenger in a minutes-long chokehold that was captured on video plans to tell his story before a grand jury in an attempt to avoid a manslaughter indictment, according to people with knowledge of the matter.

The man, Daniel Penny, would testify in his own defense next month. The move appears to reflect his lawyers’ confidence that Mr. Penny, a Marine veteran, can shape the way jurors view the highly publicized and politically charged episode on an F train earlier this month.

The grand jury, impaneled by the Manhattan district attorney’s office, can vote to indict Mr. Penny, 24, in the death of Jordan Neely, a 30-year-old former Michael Jackson impersonator who relatives said had long been battling severe mental illness.

The case’s racial dynamics — Mr. Neely was Black and Mr. Penny is white — and the decision by the police not to immediately arrest Mr. Penny made it an instant flashpoint in New York City and beyond.

Mr. Penny’s cause has been championed by some conservatives and become a talking point for Republican contenders for the 2024 presidential nomination. Mr. Penny, they argue, was protecting his fellow passengers, and his prosecution is unjust.

Progressive leaders have said the killing and Mr. Penny’s delayed arrest are evidence of a racist justice system — a position echoed by protests in the wake of Mr. Neely’s death. And many have pointed to structural problems they said the killing brought into focus: insufficient care for people with mental illness, and New York City’s failure to fully address safety on the subways.

Mr. Penny surrendered to the police 11 days after the killing. He was charged with manslaughter by the Manhattan district attorney’s office, which began preparing to present evidence to the grand jury.

Though Mr. Penny has been arrested and charged, prosecutors must still seek an indictment to move forward with the case. To do that, they must convince a majority of grand jurors that there is reasonable cause to believe that Mr. Penny committed a crime. The grand jury of 23 randomly selected people from Manhattan will meet behind closed doors over the next several weeks, though the exact timing of the process is unknown.

For the vast majority of defendants, a grand jury indictment is all but a foregone conclusion. Under New York law, defendants have a right to answer questions under oath before the grand jury before they are indicted, but rarely do so. Defendants’ grand jury testimony can be admitted as evidence at an eventual trial, regardless of whether they choose to testify during the trial itself.

Mr. Penny’s plan to testify signals that his lawyers feel confident that he could represent himself well in front of a grand jury.

Former prosecutors said that given the unusual circumstances of the charge against Mr. Penny, the plan to have him testify made sense.

“They’re going to be playing up the humanity of this guy 100 percent,” said Thomas Schiels, a 30-year veteran of the Manhattan district attorney’s office. “He’s got a great military background, he’s apparently never been arrested before, he’s going to be fairly well-spoken and his claim, though not a legal self-defense perhaps, is certainly going to be appealing to much of the general public.”

A spokesman for the Manhattan district attorney’s office declined to comment, as did the law firm representing Mr. Penny, Raiser and Kenniff.

On May 1, Mr. Neely became noticeably upset on an F train in SoHo, shouting that he was hungry and that he didn’t care about returning to jail, or even dying, witnesses told the police. He had a long history of arrests and, three months earlier, had pleaded guilty to assaulting a 67-year-old woman, a stranger, on the street, leaving her with a broken nose and eye socket and other injuries.

But while witnesses have said that Mr. Neely’s behavior on the train was “hostile and erratic,” there has been no indication that he physically threatened anyone, and it is highly unlikely that the other passengers knew his criminal history. The moments leading up to Mr. Penny’s actions are a likely focus for the grand jury.

Mr. Penny placed Mr. Neely in a chokehold that resembled the nonlethal maneuver taught to Marines in training. Known as a blood choke, it is designed to cut off circulation — not air flow — to the brain. Done properly, a blood choke can render an opponent unconscious in as little as eight seconds.

But a passenger began filming the two men on his phone after Mr. Penny’s chokehold was already in place, and the video shows it lasted about four minutes — continuing after Mr. Neely went limp and lost consciousness. The duration of the chokehold was noted by the prosecutor leading the case, Joshua Steinglass, at Mr. Penny’s arraignment on May 12. It is likely to be another source of interest for the grand jurors, as is Mr. Penny’s potential explanation for it.

Little is known about Mr. Penny outside of his military service, a four-year enlistment with the Marines that sent him on two deployments to the Mediterranean. He was honorably discharged in 2021, at Camp Lejeune in North Carolina. He settled for a time in nearby Wilmington, a beach town popular with surfers and newly independent Marine veterans. He was both.

He walked into a surf shop in late 2021 looking for work and was hired immediately, said a former co-worker there, Sam Santaniello, 20. He recalled Mr. Penny’s somewhat complicated relationship with the Marine Corps.

“He said, ‘It was the worst but best time in my life,’” Mr. Santaniello recalled in an interview. “I think the Marine Corps, for him, was just a way for him to travel. He loves to travel and we talked all about it.”

Mr. Penny’s lawyers have declined to make him available for interviews with the news media, with the exception of The New York Post, which spoke with him on May 20 on Long Island. Mr. Penny said then that he regularly uses the subway, and that the May 1 incident was unlike “anything I’d experienced before.”

“This had nothing to do with race,” he told The Post, declining to discuss the killing itself.

Mr. Santaniello described his friend as a detached centrist. “There’s some people in our generation that are just engulfed in politics. I don’t think either of us are,” he said. “He’s just kind of right in between. I’m sure there are ideas he likes that are on the left, and he likes ideas that are on the right.”

But he added, “I think now he’s super appreciative of just the support that he’s gotten.”

Mr. Neely’s history was much more closely documented, and his behavior and actions were regularly recorded by outreach workers in the subway system, who usually provided aid and moved on, but sometimes took him to shelters.

After his arrest in the assault on the woman in 2021, he spent months in jail, and was released to a mental health facility in February, with medication and a specific 15-month plan toward rehabilitation. But he walked away from the program just 13 days later.

Kevin Maurer contributed reporting from Wilmington, N.C.