In 1962, at 65, Thornton Wilder drove alone from the East Coast to Douglas, Ariz. His car died there, and he liked it enough to stick around for 20 months. What sent one of the greatest living American authors — the first to win Pulitzer prizes in fiction ( The Bridge of San Luis Rey) and drama ( Our Town) — to a nowhere town in which he didn’t know a soul? A case of excessive sociability.

Penelope Niven’s rich life of Wilder, which draws upon archives unavailable to previous biographers, situates him firmly in his family: old New England Puritan stock, with all the sexual repression that suggests; not much money; domineering father, artistic mother; five children, each with artistic leanings. Thornton’s designated role, once he’d withstood his father’s disdain for his alleged impractical nature and become a bestselling author, was to support them all, financially and emotionally, as needed.

Outsiders also made demands: theatrical producers (everyone wanted a new play from the author of The Skin of Our Teeth and The Matchmaker, especially after this last became the basis for the hit musical Hello, Dolly); movie bigwigs (Wilder wrote a brilliant screenplay for Alfred Hitchcock’s Shadow of a Doubt); and colleges (in letters, Wilder groused about how Harvard ran him ragged to deliver the Norton lectures in 1950). Wilder was too compliant to say no, and especially during the 1940s and ’50s, he was hard-pressed to find time to write.

In Douglas, Wilder found the chance to work unpestered during the day and to shoot the breeze with salt-of-the-earth rustics in the local taverns at night. The self-imposed exile allowed him to get started on the masterwork of his old age, his novel The Eighth Day, into which he poured his long-fermenting knowledge of the American family.

Thornton Wilder: A Life is the best sort of literary biography, one likely to send the reader back to the author’s works. In Wilder’s case, this might bring a surprise or two. Niven, who has also written biographies of poet Carl Sandburg and photographer Edward Steichen, does not solve the mystery of Wilder’s sexuality. “A case can be made,” she cautiously sums up, “that Wilder was bisexual in his emotional affinities, celibate by choice and circumstance more often than not, and private about his sexual relationships.” In any case, his work contains plenty of eros, if little overt sex.

For the most part, Niven eschews literary criticism, which means she says nothing about Wilder’s chief fault as a writer: sententiousness. Even the famous last line of The Bridge of San Luis Rey — “There is a land of the living and a land of the dead and the bridge is love, the only survival, the only meaning” — may work better as a proverb than as a fitting conclusion to the story of five lives lost in an accident. Wilder seems to have recognized this tendency in himself. In a letter, he endorsed a saying of Chekhov’s: “It is not the business of writers … to answer the great questions (let the theologians and philosophers do that if they feel they must) but ‘to state the questions correctly’ ”

As for Niven, she has admirably done what Chekhov identified as a writer’s business: stated the great questions about her subject correctly.

Dennis Drabelle reviewed this book for The Washington Post.