Stanley Plumly was already a giant among poets by the time he decided, several years ago, to turn his attention to narrative nonfiction.

He began, understandably, with a poet: “Posthumous Keats” was a “personal” biography that grew out of Plumly’s decades-long obsession with John Keats. That same passion compelled his follow-up, “The Immortal Evening: A Legendary Dinner With Keats, Wordsworth, and Lamb.” Recounting in gripping detail the night Keats met William Wordsworth, the book won the Truman Capote Award.

Now, remaining in the Romantic era but branching out into the world of art, Plumly has written “Elegy Landscapes: Constable and Turner and the Intimate Sublime,” a dual portrait of British landscape painters John Constable and J.M.W. Turner. With a keen eye for artistic composition and in language that easily alternates between analytical and lyrical, Plumly explores the two artists’ canons through the prism of their lives, all the while asking: What makes their work unique and lasting?

“Elegy Landscapes” contains 41 incisive, engaging chapters that alternate between the painters. Plumly depicts Constable as a genius whose value went unrealized during his life. Born in rural England in 1776, the son of a merchant and landowner, Constable began painting in his 20s but had trouble selling his work — a curse he suffered throughout his career. To earn commissions, he painted portraits. One early subject was Maria Bicknell; she was 12, he 24. Years later, they fell in love and married despite her family’s disapproval of Constable’s financial prospects; he often lived on an allowance from his father. “My life is a struggle,” Constable wrote to a friend, “between ‘my social affections’ and ‘my love of art.’ ” The couple had seven children.

Constable also fell in love with “his father’s land and the land around it,” Plumly writes. Or as Constable put it: “Landscape is my mistress.” That love affair produced paintings such as “The Hay Wain,” his most famous picture, and “The Cornfield,” a late masterpiece — work that Plumly calls a “meditation on the pastoral.” As his popularity grew, largely after his death, Constable’s oeuvre was viewed with such distinction that the place where he grew up — his muse — became known as “Constable Country.”

Meanwhile, Plumly portrays Turner as a self-made man deeply conflicted over his success, “a wealthy man who hates spending money.” Born in poverty in London in 1775, Turner, the son of a barber, showed artistic brilliance at a young age. Throughout his career, his work sold well, earning him a handsome living. There were three women in his life — the widow Sarah Danby, with whom he had two daughters; her niece Hannah Danby; and the widow Sophia Booth — though he never married. After Turner’s mother was committed to the Bethlehem Hospital for the insane — Bedlam — where she would die, his father, Plumly writes, “moves in with his son and becomes odd jobber, art supplier, grocery shopper, canvas preparer, cheerleader, and total parent, mother as well as father.”

Turner was obsessive about his work. Plumly quotes a story Turner told (some believe hyperbolically) about his research for “Snow Storm,” a painting of a steamboat at sea during a storm: “I got sailors to lash me to the mast to observe [the storm]; I was lashed for four hours, and I did not expect to escape, but I felt bound to record it if I did.”

Although other masterworks — “A Skeleton Falling Off a Horse in Mid-Air,” “The Angel Standing in the Sun” — may have proved less perilous to create they share a common trait. Whereas Constable preferred the concrete image, Turner chose to depict the “essence” of a landscape over reproduction. Plumly notes that “over time, [Turner] develops ghostlier and ghostlier forms” to capture what Thomas Hardy saw as “the deeper reality underlying the scenic.”

Despite differences in their lives — “Turner’s growth as an artist seems to occur at the speed of ‘genius’ [while] Constable’s evolution is stubborn, slow going, and uncertain” — they had this similarity: Each suffered a death that had a lasting effect. For Constable, it was the death of Maria to consumption. “She is dying,” Plumly writes, “very slowly but relentlessly, and has been since who knows when, her late teens likely . . . on the same street where a very young Keats and his brothers have set up house . . . finally, Maria Constable passes.” For Turner, it was the death of his father, in 1829 — a loss that caused him to suffer bouts of depression for the rest of his life.

The painters also shared this: Their work aspires to, and at times achieves, “the sublime” — “a term,” Plumly once wrote in an essay, “of breathtaking, soaring, awe-inspiring fear and fascination, a traveling word evoking out-of-the-body.” The almost indescribable sense of grandeur, meant to inspire through beauty or magnitude, is why a work lasts. Wise in its knowledge of art, readable in its storytelling, “Elegy Landscapes” documents Constable and Turner on their quest to capture the intimate sublime.

Stanley Plumly will discuss “Elegy Landscapes” at Politics and Prose on Aug. 21 at 7 p.m.

Paul Alexander is the author of seven books, among them “Rough Magic” and “Salinger.” He teaches at Medgar Evers College and Hunter College in New York City.

ELEGY LANDSCAPES

Constable and Turner and the Intimate Sublime

By Stanley Plumly. 272 pp. $29.95.