Billy Porter’s “Ghetto Superstar (The Man That I Am)” sounds like autobiography, but at heart it’s a love story, subgenre: showbiz. It recounts the tale – dizzying highs and punishing lows, triumphs and separations – of a lifelong love affair. Mr. Porter is one side of the romance; his larynx is the other.

But who doesn’t love that larynx? George C. Wolfe says Mr. Porter has a voice that comes along only once in a generation of American musical theater performers. A strong endorsement, and possibly even true. Because there certainly aren’t very many singers, of this or any age, who have Mr. Porter’s combination of gospel fervor, R&B style, and Broadway power.

Mr. Porter and his voice take the stage backed by two singers and a four-piece band. Not the usual lineup for a show at the Public Theater, but this isn’t your usual show. According to press materials, “Ghetto Superstar” marks the first time the Public has produced a show at Joe’s Pub as part of its regular season. The merits of Mr. Porter’s evening aside, the mere fact that it exists is cause for enthusiasm. With the conventional musical looking soggier by the season, the Public has taken an important step in the best traditions of its founder. Joe Papp gave New York two epochal, groundbreaking musicals, “A Chorus Line” and “Hair.” The snug cabaret space of Joe’s Pub is just right for further adventures in new musical theater.

So let it be noted that this chapter in the Public’s august history begins with Mr. Porter, dreadlocks streaming, launching into his self-penned cride coeur, “Black Broadway Bitch.” At its full length, Mr. Porter’s label for himself is “black Broadway bitch from the ghetto.” Through 20 songs (about half of which are originals) and spoken interludes, he walks us through his journey from the mean streets of Pittsburgh to major multiformat talent to finding peace with himself. It’s easier to be enthusiastic about the voice telling the story than the story itself, which doesn’t always captivate. Still, the show is sometimes funny, sometimes harrowing, and always well sung.

What it’s definitely not is self-deprecating. “I am what I am,” Mr. Porter declares, “and I stand proudly.” I’ll say he does. Any self-esteem troubles he may have faced earlier in life seem to have been vanquished. (Of course, the solo autobiographical show is not well suited to the meek or especially humble.) In the first few minutes, he says he was called a genius before age 10. After some success on stage, screen, and in music, he describes himself as a diva. The emblem of Mr. Porter’s self-acceptance is a pair of improbable red high heels.

Mr. Porter was raised for a time by a single mother (before a stepfather arrived, bringing a world of troubles), in a Pentecostal home. The hymns and services were helpful for honing his voice, less so his sexuality. As a gay, black young man, Mr. Porter faced what sounds like endless torture (it’s not too strong a word). His homosexuality would later cause no end of grief among the record executives who tried to shape his career.

Salvation came to young Billy in an unlikely form: Jennifer Holliday. While doing dishes one night, he saw a clip from “Dreamgirls” on the 1982 Tony Award telecast. “This was like church,” he marveled. Musical theater, he knew, was the life for him. Even more than he had as a boy, Mr. Porter would come to rely on that golden larynx of his: “my voice, my weapon, my savior.”

The people who pay to see a well-known actor/singer/writer perform a show about his life in a New York cabaret space, it may be assumed, are not indifferent to the mythology of Broadway. The crowd perks up for Mr. Porter’s stories about breaking into showbiz in the 1980s. He tosses off sharp imitations of Ms. Holliday and others, and flings himself around the stage dancing to period-specific tracks like “Maniac.”

There are plenty of showstoppers here, the good kind and the other. Again and again, he’ll end a song with a series of high, loud, long notes that would wreck many (any?) a lesser talent. But the story also leads Mr. Porter to recount episodes of homophobia, sexual abuse, and career collapse. Director Brad Rouse helps him find these dark places – dark, quiet places. Mr. Porter sometimes visits them a cappella.

A funny (not ha-ha funny) tension grips the audience at those moments. On the stage before you stands a man excavating his soul, describing the most wrenching experiences of his life; on the table before you sits dinner. A sense of decorum dictates that you resist the urge to reach for your drink in these stretches, because the ice might clatter in the glass, and 20 people might hear it, including the star. Mr. Porter’s weighty story is sometimes at odds with his informal hall.

The solution, I think, is banter. Particularly on a cabaret stage, it’s amazing what a little give-and-take will do. “Full out I gave it to ya,” Mr. Porter huffed after one particularly explosive number, catching his breath. When he’s relaxed and easy, Mr. Porter’s byplay wins us over – we’ll follow wherever he leads. Maybe not as far as the tearful speech he delivers in his mother’s voice around the 90-minute mark, but pretty far.

How do you balance speech and song, seriousness and chit-chat, in this kind of theater? What kind of show might result? It’ll take some exploring to find out. Here’s hoping the Public keeps giving composers and playwrights a chance to do so.

Until March 27 (425 Lafayette Street, between E. 4th Street and Astor Place, 212-254-1263).