About two-thirds into Laura Dassow Walls’s extraordinary new biography of Henry David Thoreau, she relates an anecdote that tells us more about the man than many a scholarly tome. On one of his many walks in or around Concord, Mass., a passerby accosted him: “Halloo, Thoreau, and don’t you ever shoot a bird then when you want to study it?” Snapped back Thoreau: “Do you think that I should shoot you if I wanted to study you?” Study the living being, not its dead shell. And this is precisely what Walls has done in her definitive life of this opinionated, often difficult, but always interesting writer, who was so excited to have been born into just the right place and, as he said proudly, “in the very nick of time.”

Great biographies are never just about the life of a particular man or woman, but about life itself. And, as it happens, life was also the primary object of Thoreau’s quest. In a much-excerpted passage from his 1854 masterpiece, Walden; or Life in the Woods, he claimed that he wanted nothing more than “to drive life into a corner, and reduce it to its lowest terms,” as if it were a wild animal that could be trapped, contained, and tamed into obedience. Which, as Thoreau was happy to admit, would have been impossible.

To her great credit, Walls gives us so much more than the quotable Thoreau, the bane of the American literature survey course. Undergraduates, it is true, invariably dislike Thoreau. If you are getting ready to interview for the job that might change your life, the last thing you want to hear is Thoreau’s advice that new clothes are less important than the person who wears them. Thoreau hated fashion and the pressure it put on people’s self-esteem: “The head monkey at Paris puts on a traveller’s cap, and all the monkeys in America do the same.” But tell that to an interview committee. And his professed aversion to philanthropy—“A man is not a good man to me because he will feed me”—usually puts off the more progressively minded students in the classroom.

Of course, as I try to explain to my students, Thoreau never meant to discourage us from dressing well or from helping other people. Instead, he wants us to question a system in which external conformity replaced inner identity, in which fleeting effects are more important than durable motives: “If you give money, spend yourself with it.” While Walls briefly registers her impatience with Thoreau’s critics—those who think he was a hypocritical mama’s boy who didn’t do his own laundry and enjoyed dinner at the Emersons’ rather than eating his homegrown beans at Walden Pond—she fortunately spends little time defending him. Instead, she immerses herself and her readers fully in Thoreau’s environment, the fields, meadows, woods, and streets of Concord. Walls’s book is, first and foremost, the product of an extraordinary act of empathy. But it is also an outstanding literary achievement. No biographer has more credibly evoked those blisteringly cold, crystal-clear New England winter days, days that, thanks to Walls’s prose, sparkle, glimmer, and chill for us the way they once did for Thoreau, when, rising early, he had to first thaw his ink before he could begin his writing. The air was so cold that at night, bedsheets would freeze around people’s faces. And those who ventured out during the day often couldn’t fully button their coats since their fingers were too numb. “Everyone marveled at the cold,” writes Walls. “Marvel” is a beautifully appropriate word here. Imagine the same sentence with a different verb, and it instantly disappoints: “Everyone was astonished by the cold.” But what really carries the whiff of 19th-century small-town New England is Walls’s “everyone,” a reminder of a time when the weather temporarily leveled differences between the rich and the poor, the young and the old, and all would stare in mute wonder at the transformed landscape.

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And yet Thoreau was not everyone. How odd he must have seemed when one encountered him on the road: a small, wiry man with piercing blue eyes, his pockets weighed down by all he carried around with him—a jackknife, twine, pencils, telescope (to see the birds), microscope (to count the stamens of the flowers he found), and diary (to write down what he had found). Emerson probably never fully understood him, a thought that pained Thoreau, who lamented that their friendship was a “tragedy of more than 5 acts.” “Ugly as sin” his sometime neighbor Nathaniel Hawthorne called him, while Hawthorne’s son Julian, one of Thoreau’s walking companions, settled for the somewhat kinder “unbeautiful.” Of course, Thoreau, throughout his life, was surrounded by other very odd people—moody Ellery Channing, for example, as uneven a poet as he was a father and husband, and the formidable Sophia Foord, 15 years older than Thoreau, who alarmed him with her marriage proposal. Even though Foord was immediately rebuffed, she swore that she was Thoreau’s soulmate and that her spirit would join his in the afterlife.

The great imaginative accomplishment of Walls’s book is to put Thoreau firmly back into the community that fostered and, for the most part, protected him. Unmarried aunts, uncles, and siblings were common in Concord, and Thoreau’s secret (if a secret it was), his preference for men, was safe with his fellow townspeople. Walls’s approach to Thoreau’s sexual identity is a model of biographical probity. Although Thoreau wrote constantly about Thoreau (if only, he quipped, because he didn’t know anyone better than himself), he rarely let his guard down. Walls is right to point us to an agonized passage written after Thoreau had returned from Mount Katahdin in Maine: “Think of our life in nature,—daily to be shown matter, to come in contact with it,—rocks, trees, wind on our cheeks!” Thoreau’s prose becomes almost shrill, a cry for company, so easily withheld from the lonely soul: “Contact! Contact! Who are we? where are we?” This is a preview of Leaves of Grass, a powerful anticipation of that pivotal moment in Walt Whitman’s famous poem, published just a few years later, when the speaker longs for the wind to softly caress and tickle him. Thoreau’s best pages bristle with the same furious energy that dispels any idea that they are just the awkward products of sublimation. However, as Walls simply and beautifully clarifies Thoreau’s dilemma: “In another place and time, he might have found his life’s partner with a man.”

It was life in all its forms, human and nonhuman, that attracted Thoreau, from the forest seeds in the ground to the squirrels that distributed them to his Penobscot guide Joe Polis, who knew his way around the vanishing Maine wilderness yet took pride in his neat house and took the Bangor newspaper. Thoreau became angry when James Russell Lowell, the editor of the Atlantic, deleted a key statement from his manuscript “Chesuncook”: “A pine cut down, a dead pine, is no more a pine than a dead human carcass is a man.”

But even as he pleaded for the status of trees, Thoreau continued to be haunted by the specter of human suffering. For a long time, his house had been a trusted stop on the Underground Railroad. In a touching account by the abolitionist Moncure Conway we learn how tenderly Thoreau, often suspected of being a cold fish, would treat a trembling fugitive who had shown up at his doorstep during “slave-hunting time.” Thoreau never forgot that other, less-privileged people had preceded him at Walden Pond, notably old Zilpah White, a slave until the revolution, who built her one-room house in the woods long before Thoreau put his hoe into the ground nearby. Living a hardscrabble life, White survived by making baskets and spinning linen for the citizens of Concord. Someone—perhaps English soldiers out on parole—set fire to her house, killing her dog, her cat, and her chickens. But Zilpah White carried on. At least one of Thoreau’s contemporaries still remembered her as she survived out there in the woods, next to her steaming pot, singing and repeating to herself what Thoreau, throughout it all, knew, too—that, whatever we think our differences might be, they run only skin-deep: “Ye are all bones, bones!”

Christoph Irmscher, provost professor of English at Indiana University, is the author, most recently, of Max Eastman: A Life.