A obsession to discover the truth about an obscure singer-songwriter brings surprising and affecting revelations in Mark Bendjelloul’s “Searching for Sugar Man,” a film that would make an excellent double bill with Raymond De Felitta’s “’Tis Autumn: The Search for Jackie Paris.” But it goes that pleasant documentary one better by showing how its subject also played—unconsciously—an important role in one of the most remarkable historical transformations of the twentieth century.

The artist in question was Sixto Rodriguez, discovered in a small Detroit bar by Dennis Coffey and Mike Theodore, who produced his first album, “Cold Fact,” in 1970. Released by Clarence Avant’s Sussex Records, the album, though critically acclaimed, bombed, and Rodriguez quickly faded into obscurity. Somehow a rumor began to circulate that he had committed suicide onstage, either by shooting himself or by self-immolation.

In the meantime a copy of the record somehow found its way to South Africa, then an international pariah because of the government’s refusal to abandon the apartheid system, and as an internal movement against the regime began among disaffected whites, it adopted several of Rodriguez’s songs as its anthems. The singer became in many respects the voice of the opposition, despite official efforts to suppress the record’s more offending tracks. Not only was he the inspiration for many rebel music groups that emerged during the struggle against apartheid, but his South African fame came to exceed that of other icons in the field—including Elvis Presley.

Eventually apartheid died in South Africa but the popularity of Rodriguez there did not, and Stephen Segerman, who’d gotten his nickname of “Sugar” from the Rodriguez song “Sugar Man,” spearheaded a search for genuine biographical data on the singer, about whom little was actually known beyond his name. He and his associates even set up a website requesting information, and one day he was contacted by one of Rodriguez’s daughters, who informed him that the singer was still alive in Detroit. Eventually he came to South Africa to perform in concerts where astonishingly large crowds came out to hear the man who’d been living a simple live for decades, unaware of the level of popularity his record had achieved on another continent.

There are no spoilers here; Rodriguez’s first tour of South Africa occurred in 1998, and “Cold Fact” has been reissued on CD (along with tracks from his second album “Coming from Reality”). So while Bendjelloul constructs his film as a detective story, he’s actually a Johnny-come-lately to it, relying on archival footage to recreate the narrative. But to some viewers the revelation may still come as a surprise, and the picture works on that level.

More importantly, though, the writer-director, who also edited the film, has interviewed Rodriguez, his daughters, his one-time discoverers and producers, friends from the Detroit construction industry and bar scene and journalists, as well as Segerman and other South African fans (like guitarist Willem Moller, who actually got to play backup for his idol in the South African concerts), archivists and record executives, and includes ample footage from them. What emerges is a warm portrait of a remarkable man who seems equally comfortable with his simple life and his new-found foreign fame, as well as a historically revealing portrait of the contribution that music made to the anti-apartheid movement. Tangentially it also points to the vagaries of the American music business, with Coffey, Theodore and Steve Rowland (who produced Rodriguez’s second album) all expressing their incredulity that work of such quality was unsuccessful at the time and Avant cannily sidestepping questions about where the royalties paid to Sussex by South African companies went, since Rodriguez never saw a cent of them.

So for those unacquainted with the story of Sixto Rodriguez, “Searching for Sugar Man” will work as a particularly intriguing—and ultimately uplifting—version of an “Unsolved Mysteries” episode. In that regard it’s comparable to De Felitta’s film, as well as (to change mediums), Mark Moskowitz’s “Stone Reader” (about the author of a forgotten novel that, coincidentally, had also appeared in the early seventies). But it goes further in situating the singer’s story within the context of South Africa’s own civil rights struggle, giving it greater resonance.

And it features some fine music, too. By the time it’s over you’ll agree with those who argue that comparisons of Rodriguez’s haunting songs to Bob Dylan’s aren’t all that farfetched. Search out this fine, fascinating, warmhearted documentary.