When actor Marchánt Davis talks about the saxophone being his “weapon of choice” during his elementary school days in Nicetown, he doesn’t mean he preferred its dulcet tones to the clarinet.

He means that getting to and from school in the often rough and tumble neighborhood sometimes meant using the sax for personal defense.

“What can I say, that was Nicetown,” said Davis, star of the new movie The Day Shall Come, who manages a laugh when he thinks back to those days — days that also included asking his folks for paper so he could print out his assignments to make up for the fact his school didn’t have enough books.

“I’m not going to learn here,” he remembers saying to his parents, so they got him transferred to Shawmont elementary in Roxborough. The school had a strong music program, but Davis found that his enthusiasm for the intended use of the saxophone did not increase. The city, via Davis, would not produce another Coltrane.

He remembers a teacher, Miss Clark, telling him “Look, you never practice, maybe should find something you want to do more.”

He turned to musical theater and acting, the commencement of an incredible journey that’s led Davis not only to a lead role in the new movie The Day Shall Come (by British satirist Chris Morris, Four Lions) opening here Friday, Oct. 4, but a major role in the Broadway production of The Great Society. He’s playing Stokely Carmichael, alongside Brian Cox’s Lyndon B. Johnson, in a sequel to the Tony Award-winning All The Way, also written by Robert Schenkkan.

The springboard for all of it were those early days at Shawmont and middle school, where he starred in a seventh-grade production of Annie, playing Rooster.

“The next thing I know, everybody is saying ‘Oh my God, he needs to be an actor,’ and that became my path,” Davis said. From there it was on to the Philadelphia High School for Creative and Performing Arts, where on shadow day, a ninth-grader named Leah Hawkins noticed a wide-eyed visitor — the eighth-grade Davis — staring at everybody, taking it all in.

When he showed up the next year, she introduced herself, and they became close friends.

“It was immediately clear that he was the kind of person who would push through,” Hawkins said. “We both were, and we connected, and you really need that support, because you need someone who understands what you’re going through.”

It obviously benefited both of them — Hawkins, who went on to get her master’s in vocal arts at Yale, just opened at the Metropolitan Opera in New York as Strawberry Woman in the new production of Porgy and Bess, which stars Philadelphia native Eric Owens as Porgy.

“It was absolutely clear that he had talent. And was not just a singing actor. He could handle straight drama.” she recalls of Davis, who at CAPA had roles in Fiddler on the Roof and Singin’ in the Rain. He was a high achiever who also found time to be student body president and a Bible study leader.

So it tracks that he won a scholarship to Boston Conservatory, and went on to New York University’s Tisch School of the Arts. Upon graduating, he started auditioning for film and theater roles. Six months and 100 auditions later, he sat down with Morris, who was looking for a Moses, the lead in The Day Shall Come. It’s an edgy satire of an overzealous FBI investigation of a group of eccentric outcasts in Miami misidentified by the feds (Anna Kendrick, Denis O’Hare) as a potential terror group. It’s loosely based on the Liberty City Seven, a group of Miami men who lived in the Liberty City projects in Miami and who were charged with terrorism.

Davis said it was more of an interview than audition — Morris was keenly interested in Davis’ accounts of the MOVE organization in Philadelphia, the Fletcher Street Urban Riding Club, and his mother’s habit of buying white Santas and painting them black for the holidays.

Those details turn up, in various forms, in the film.

“He said, ‘I have this idea of Moses riding in on a horse. Can you ride?’”

Davis again had his mother to thank — for the several years she sent him to “white people’s summer camp” in New Jersey, where he also learned to shoot a crossbow, helpful in case Game of Thrones ever comes back.

It all fed his collaboration with Morris to create the character of Moses.

“What a blessing. Here you have this famous British director, asking my opinion, but his attitude is, if you have the knowledge and something to contribute, I want to hear it.”

He also got support from the cast, including veteran character actor O’Hare, who kept teasing him about being No. 1 on the call sheet (a ranking of leads and supporting players).

“Denis would say, ‘I’m a four or a five. Sometimes a three. But you’re No. 1. We’re going to be looking to you to set the tone,’” Davis said. “That sounds like pressure, but it was a great way to get rid of anxiety, because he said, ‘We’re going to work with you.’”

They had a good time on set, but never lost sight of the seriousness of the film’s subject.

The real-life Liberty City prosecutions resulted in several mistrials and acquittals before the feds got convictions on some members of the group. Juries were receptive to defense arguments that the Liberty City targets were stringing along FBI informants and undercover agents posing as al-Qaeda — gaming them for as much money as they could get with fictitious plans to blow up the Sears tower.

Davis sees clear parallels to his next gig in The Great Society, which officially opens Oct. 1, and the way LBJ was threatened by Carmichael’s efforts to establish the Mississippi Freedom Democratic Party and independent political organizations to empower black voters, and for his efforts was targeted by J. Edgar Hoover’s FBI.

“What happens in our movie, and what was going on COINTELPRO in the 1960s, those links are very striking,” Davis said. “It’s exciting to be able to do work that has something to say.”