Amara Fofana is among the list of people responsible for collaborating on the screenplay for the new film by Italian director Matteo Garrone, “Io Capitano.” In 2013, Mr. Fofana left his native Guinea on a trek to reach Europe. After having passed through Mali, Niger, and Libya, he commandeered a boat containing 250 migrants and sailed to Italy. This responsibility was the payment due to traffickers for his passage.

Mr. Fofana was 15 years old at the time. He didn’t know how to swim and had never captained a boat. All the same, he brought his charges, safe and fairly sound, to the shores of Sicily. Upon approach, Mr. Fofana began shouting, “I’m the captain! I’m the captain!” The traffickers assured him that he wouldn’t be taken into custody because of his status as a minor. They were wrong: Italian authorities arrested Mr. Fofana, having mistaken him for a smuggler.

Mr. Fofana was subsequently released and is now living in Belgium. “Io Capitano” is not his story alone, but a compilation of narratives provided by others who made similar journeys. “It became crucial,” Mr. Garrone emphasizes, “to not simply re-tell these stories, but to have those who lived them … at my side during production.” The director’s quest for authenticity has occasioned a film of heroic scope and harrowing brutality. It has been nominated as Best International Feature for this year’s Academy Awards.

Another collaborator vital to the film’s integrity was born at Ivory Coast and now does social work in the south of Italy, Mamadou Kouassi. Like Mr. Fofana, Mr. Kouassi was a teenager when he crossed the Sahara Desert seeking a better life. The bodies of dead and dying migrants along the sand dunes were only part of a story whose travails are difficult to fathom. Mr. Kouassi was apprehended by the Libyan mafia, imprisoned, tortured, and sold into slavery. Three years later, he arrived in Europe, a stowaway eager for freedom.

At the center of “Io Capitano” is Seydou (Seydou Sarr), a teenager living in Dakar with a single mother and a host of younger siblings. The house in which he lives is threadbare and shabby; the surrounding township, much the same. Moments of joy — playing drums during a local holiday, say — are rare in this poverty-stricken neighborhood. Seydou huddles with his cousin Moussa (Moustapha Fall) and watches videos from Europe on his smartphone. Dreams of pop stardom enter their heads. 

Unbeknownst to their families and friends, Seydou and Moussa have been doing construction work, saving their pay in order to buy passage out of Dakar. Seydou’s mother (Khady Sy, by turns ebullient and ferocious) gets wind of their plans and doesn’t take them lightly. Neither does a vendor at the local marketplace, Sisko (Cheick Oumar Diaw). Both adults don’t caution the boys so much as scare the bejesus out of them. Which, of course, only goes so far with headstrong teenagers.

After receiving the go-ahead from spirits summoned by a shaman (Doodou Sagna), Seydou and Moussa steal away in the night, starry-eyed and eager. Whereupon they encounter a hellish array of obstacles that Mr. Garrone has, apparently, toned down for public consumption. Be warned that this remarkable film doesn’t stint on depicting the horrors our two heroes undergo. Then take note that the two actors who embody them are new to the medium. No actor in the film, most of whom are untrained, strikes a false note. Mr. Seydou has already racked up awards for a performance that is utterly without guile. 

Let’s see if “Io Capitano,” a film of unapologetic optimism and rather old-fashioned at that, is bestowed with another award come this March at the Academy Awards. In the meantime, Mr. Garrone has crafted a film of breathtaking and, in the end, humbling proportions.