Over the last decade or two, we’ve seen the Hollywood biographical drama — once the cheesiest of genres, though often an irresistible one — mature as a popular art form. The key evolution, dating back to films like “Capote” and “Lincoln” (and extending through “Oppenheimer”), was the decision to ditch the old cradle-to-grave sprawl in favor of focusing on a crucial time period of someone’s life — a strategy that allows for more texture and truth.

“Bob Marley: One Love,” a drama about the most larger-than-life of all reggae superstars, ardently follows the new biopic rules. The film opens in 1976, when Bob Marley (Kingsley Ben-Adir), lean and majestic in his bouncing dreadlocks, heading toward the height of his fame, is getting ready to play a peace concert in Kingston. His goal is to heal the violent factionalism of Jamaican politics. It’s an uphill battle. The Jamaica we see is a war-torn mess — a morass of post-colonial chaos, with rival political parties and gang leaders fighting for turf. Even Marley can’t seal himself off from the violence. Before the concert, a pair of gunmen break into his compound, where they shoot his wife, Rita (Lashana Lynch), in the car and attempt to assassinate Marley. The two are lucky to escape — Marley with barely a flesh wound, and Rita, though she lands in the hospital, recovering quickly. But this is clearly a sign. The time has come for Marley to leave Jamaica and take stock.

“One Love,” directed by Reinaldo Marcus Green (“King Richard”), is set over the following two years, during which Marley lands in London. There, despite getting arrested for the crime of looking the way he does, he carries on a relatively serene and hassle-free existence as he reunites with his band, records the album that will become “Exodus,” hobnobs with the swells, and reassesses his place in the global pop universe.

On paper, one understands why this period of Bob Marley’s life might seem fertile for filmmakers. It’s about laying bare the contradictions that define Marley — the political militant who is also a utopian pop idol, the family man who depends on Rita yet is anything but faithful to her (he has children by other women), the devout Rastafarian who uses religion, and the Ethiopian guru figure of Haile Salassie, as a substitute for the white British father on horseback who abandoned him. Marley, as both a musician and a man, is steeped in Jamaica (its politics, poverty, and trauma). Yet as he centers himself in the exile of London, and as “One Love” turns into a rambling and rather haphazard mid-’70s hang-out movie, the film looks at how Marley evolved into a grander figure, a shaman star whose message of liberation began to transcend national boundaries.

At least, that’s the idea. But here’s why “One Love” is a movie as problematic as it is provocative.

By limiting itself to the period of 1976-1978, the film shows us almost nothing of how Marley rose up in Jamaica and helped to forge the inside-out-rock-‘n’-roll form of reggae, building on its roots in ska and rocksteady and R&B. There are a handful flashbacks to Marley’s early days (including an engaging recording-studio scene in which his formative band, the Wailing Wailers, gets a groove going as they perform “Simmer Down”). But given that this is Hollywood’s first major reggae biopic, what we yearn to see is how reggae took off and gained power as an art form. That the film treats all this as ancient history, turning songs as incendiary as “Get Up, Stand Up” into generic needle drops, is baffling and weirdly unsatisfying. The screenplay is credited to four writers (Terence Winter, Frank E. Flowers, Zach Baylon, and the director), and given what an anecdotal patchwork of a script it is, that suggests there was a lot of rewriting. Yet the process never yielded a compelling structure.  

From the moment you first see him, Kingsley Ben-Adir inhabits Marley with the finesse of a movie-star showman. Ben-Adir studied dozens of hours of tapes of Marley to nail every nuance of his patois, and while the result is that audiences may miss some lines (50 years ago, “The Harder They Come” was subtitled), you feel Marley come alive as a presence. The actor captures Marley’s messianic lilt, his playful way of keeping his real agenda private. And when he dances on stage, locked into the rhythms like a rag-doll revolutionary, Ben-Adir’s Marley is a mesmerizing figure — a total pop star, though more than other pop stars he gives you the sensation that he’s channeling a spirit larger than himself. Yet even the pleasure of the concert scenes remains scattershot. They don’t build.

Along the way, the film touches on such disparate subjects as Marley’s passion for soccer, the rise of the Clash (whose influence by reggae is never mentioned), Marley’s desire to do a tour of Africa, his indifference to looking after his health after he receives a diagnosis of melanoma (the cancer that killed him in 1981), and the austere album cover art for “Exodus” (Michael Gandolfini plays a callow record-company executive who can’t bear the thought that Marley’s image won’t be on it). According to a closing title, Time magazine chose “Exodus” as the greatest album of the 20th century (I don’t even think it’s Marley’s greatest album), but the movie asserts the importance of the record without demonstrating it.

Too often, “One Love” feels like the downbeat, neurotic middle act of a conventional biopic — the hero lost in his identity crisis, hemmed in by fame — stretched out to feature length. The film tells you a lot about Bob Marley, yet it never quite figures out what his journey is. Lynch’s Rita is the movie’s most grounded character; her devotion to Marley, coupled with her understanding of his pain, is moving. But except for the scene in which Marley violently attacks his manager for trying to milk an African tour for profit, the Marley we see is close to a saint. The point of the new biopic mode was to reveal totemic figures in a more complex way. “One Love” flirts with complexity but slides into the banality of hero worship.