More than any writer of his era, Kurt Vonnegut survives as an image: haggard, mustachioed, nicotine-stained, his hair a tangle—a cat’s cradle, one might say—of curls. As was often noted, he looked like Mark Twain, only cuter. Certainly, he was more boyish than Twain. He was a millionaire who rued, until he died, that his mother had not been a better hugger; a grown man who went swimming, sheepishly, in pants; a father who “painted pertinent quotes on various walls in the house.” He was 6’3″, but small at heart. “If the government assigned heights based on maturity,” he wrote in a letter to his first wife, Jane, “[I] would be much shorter.”

Vonnegut’s fiction was similarly deceptive; he addressed major themes in a minor key. “Mass destruction was a bit of a Vonnegut trope,” as Charles Shields observes in And So It Goes: Kurt Vonnegut: A Life (Henry Holt and Co., 528 pages, $30.00). That this was so is undeniable, and yet the message of Vonnegut’s darkest novels must sound saccharine to many schoolchildren. He believed in common decency and common sense, in mankind over machines. He was big on being nice. Being nasty was a bête noire. To the madness of his century, Vonnegut, who died in 2007, applied the moral vision of a Mouseketeer.

This made him a sympathetic public figure, who was quick to decry the religiosity of the Republican party and the war in Vietnam, but a novelist whose limitations were as conspicuous as his gifts. “There is an almost intolerable sentimentality in everything I write,” as Vonnegut himself admitted. In his greatest satires, Cat’s Cradle (1963) and Slaughterhouse-Five (1969), he envisioned catastrophic events from the perspective of their bystanders. This reflected a truth of his own experience. As an American prisoner of war in Dresden, in 1945, Vonnegut had hidden in an underground meat locker while Allied aircraft firebombed the city. When he emerged, “Lazarus-like,” days later, Dresden was a cinder. “It was as if he had slept through the sacking of Troy and woke just as the Greeks were boarding their ships for home,” as Mr. Shields puts it.

Vonnegut’s genius was to stake out this experience of anticlimax as his novelistic territory. His heroes are bemused bit players whose lives are measured by their distance from great affairs, rather than their proximity to them. It is a worldview inverted in favor of the little guy, and it is as hostile to change as it is to power. Mr. Shields is insightful when he points out that Vonnegut, though revered by hippies, was “less a radical than a reactionary.” On the day of the moon landing, in 1969, Vonnegut went on the CBS Evening News with Walter Cronkite, where he could rail against its profligacy in real-time. “For that kind of money,” Vonnegut had already written, paraphrasing a scientist, “the least [NASA] can do is discover God.” He had become the lord of the bumpkins. And indeed, with his frayed Afro and slight stoop, his invariable cigarette, Vonnegut looked the part.

It is surprising, then, to discover the degree to which this look and the persona that went with it were contrived. Mr. Shield’s biography of Vonnegut takes its title from Slaughterhouse-Five, where it occurs dozens of times; it is the perennial refrain of bad news. “He was arrested for plundering. He was tried and shot. So it goes.” The phrase encapsulates the attitude of wistful passivity that readers correctly associate with Vonnegut’s fiction. But it is an ironic title for the biography of the man himself, because Kurt Vonnegut the illustrious author was a strenuous work of artifice, whose fate was anything but thrust upon him. “We are what we pretend to be,” Vonnegut wrote in his third novel, Mother Night (1961), “so we must be careful about what we pretend to be.” He was a scrupulous pretender who heeded his own advice.

Vonnegut was born in Indianapolis in 1922. He grew up in a milieu so mistrustful of art that, when it came time for him to go to college, he was compelled, against his wishes, to study chemistry. Yet he discovered his vocation early. Vonnegut wrote columns for his high school and college newspapers, and, after the war, in 1951, he quit a well-paid job in public relations at General Electric to pursue his fiction full-time. But he was already married and a father, and he continued, perforce, to supplement his income by less exalted means. He worked as a high school teacher, a creative writing instructor, a copywriter, a car salesman and a caption writer for Sports Illustrated, where his tenure was characteristically brief. “The horse jumped over the fucking fence,” Vonnegut wrote the day he walked out. He was rarely too proud to stoop to an opportunity, but often too proud to exploit one. “Maybe the problem was not that the agents didn’t know what to do for [Vonnegut],” the SI secretary, Carolyn Blakemore, later reflected, “but he didn’t know what to do in the role of a writer.”

Ms. Blakemore misjudged her colleague. One thing Vonnegut did do was rise at 5 every morning to write. And when his moment finally came, he seized it with an alacrity that is hard to distinguish, in Mr. Shields’s telling of the story, from opportunism.