At more than 650 pages long, Anthony Sampson’s authorized biography “Mandela” (Knopf, $30) runs the risk of overwhelming readers. Though a few may find the intricacies of South African politics overdone, most will feel the amazing balance and tempo of this work, a biography that never forgets it has a story to tell.

Sampson met Nelson Mandela in 1951 while both worked in Johannesburg: Mandela as a young lawyer and political activist, Sampson as editor of Drum magazine. Using this friendship, interviews ranging from Winnie Mandela to F. W. de Klerk, and access to previously unpublished correspondence, Sampson captures the broad sweep of Mandela’s life.

The author of nearly 20 books, Sampson constantly finds the small but telling moment. Whether showing us Mandela’s early childhood upbringing with ubuntu — an African notion of human brotherhood — or Mandela’s insistence on making his bed and doing his dishes on the cusp of release from prison, Sampson picks images that help define the man. Bit by bit, we see Mandela’s 27 years of incarceration forge his “commitment to reconciliation and forgiveness,” while Winnie Mandela’s briefer arrests and imprisonment only incite her to greater extremes.

But we also see the young inexperienced Mandela, the one who sought communist support while underestimating his Afrikaner opponents, and the older wiser president, often criticized for not using enough personal authority as he tried to establish a democratic tradition in which no single voice could dominate.

Though Sampson’s admiration for Mandela may tilt a few events in the former president’s favor, overall, this biography is a work of subtlety and craft. Sampson’s pages flow along, logically, clearly, convincingly, and we learn that Mandela proofed early drafts for accuracy of fact and detail. Sampson reminds us that the judgments and interpretations of the work remain his own. So too, does his daunting