Almost six decades after her death, Sylvia Plath stands as the most consequential poet of her generation. As a feminine voice, she dominates the 20th century the way Emily Dickinson did the century before. At the time of Plath’s death at age 30, critic A. Alvarez wrote, “The loss to literature is inestimable.” The years have proved him right.

Because of the importance of her work — her “Collected Poems” won the Pulitzer Prize and her novel, “The Bell Jar,” is a coming-of-age classic — and because of the sensational circumstances of her death, an extraordinary amount of attention has been paid to Plath in both the academic and mainstream press. So many biographies have appeared that Janet Malcolm produced “The Silent Woman” (1994), a study of Plath biography, with writers like “Bitter Fame” author Anne Stevenson suffering Malcolm’s brutal hit-and-run treatment.

Now, into the breach, comes Heather Clark’s “Red Comet: The Short Life and Blazing Art of Sylvia Plath,” an exhaustively researched, frequently brilliant masterwork that stretches to 1,072 pages (including notes). It is an impressive achievement representing a prizeworthy contribution to literary scholarship and biographical journalism.

“Red Comet” thoroughly chronicles all stages of Plath’s life. An idyllic childhood on the Massachusetts coast near Boston was shattered by the early death of her father, Otto Plath, a biologist who misdiagnosed himself with cancer only to die of — as Clark reports finding in the death certificate — “diabetes mellitus and bronchial pneumonia, due to gangrene in the left foot.”

Plath’s now-single mother, Aurelia, moved with the children, Sylvia and Warren, to Wellesley, Mass., where Sylvia graduated from high school. Plath’s stellar academic career at Smith College, a school for women in Northampton, Mass, was marred in the summer of 1953 by an unsettling guest editorship at Mademoiselle that led to a nervous breakdown and a suicide attempt. “I swallowed quantities [of sleeping pills] and blissfully succumbed to the whirling blackness,” Plath wrote to a friend. These events later inspired “The Bell Jar.”

Plath’s marriage to poet Ted Hughes, whom she met while on a Fulbright scholarship to Cambridge University, produced two children (Frieda and Nicholas) and two historic bodies of work. But the marriage’s end caused a searingly intense unhappiness that ultimately consumed them both. The unraveling began in May 1962 in Devon, where the Hugheses were living in a thatched-roof country house. Assia Wevill, an aspiring poet, and her husband, David, a Canadian poet, who were subletting the Hugheses’ London flat, came for a visit. “Ted kissed me in the kitchen, and Sylvia saw it,” Clark quotes Assia as telling David. It was the start of an affair.

The following months saw Plath descend into despair as she endured what she viewed as Hughes’s continued betrayal. While still seeing Assia, he began dating Susan Alliston, also an aspiring poet. That Hughes was simultaneously pursuing two women known to Plath was a source of acute humiliation. A breaking point came in early 1963 when Plath learned that Assia was pregnant.

The cacophony of emotions generated by Hughes’s romantic entanglements were made worse by hardships resulting from the weather — the harshest winter to hit London in a century meant frozen pipes and no heat — and her medication, a cocktail of four drugs that made her more, not less, depressed.

Living again in London, her “madness” having returned, Plath decided to end her life. On the morning of Feb. 11, 1963, with her children secured in an upstairs bedroom, she sealed herself in the kitchen, lay on the floor, and turned on the gas in the oven. “As she died,” Clark writes, “the sun rose out the large window to her left, flooding the kitchen with light.”

Portions of “Red Comet” are deeply moving, but a tendency to downplay Hughes’s violence will likely attract critics. In May 1958, when Plath was teaching at Smith, she saw Hughes strolling on campus with a student. The ensuing altercation caused Plath to report in her journal that the fight left her with a strained thumb and Hughes with claw marks on his cheeks. “I remember,” Plath wrote, “hurling a glass with all my force across a dark room; instead of shattering the glass rebounded and remained intact: I got hit and saw stars.” Clark writes of the passage: “Plath’s colon suggests that she ‘got hit’ by the ricocheting glass, not by Hughes” — a conclusion contrary to the one many other readers have reached. Another episode, which Plath described in no uncertain terms, occurred in February 1961, when Hughes beat Plath so severely she suffered a miscarriage. “Red Comet” reviews the evidence but offers an apologia from Frieda Hughes, who contends that “my father was not the wife-beater that some would wish to imagine he was.”

On that point, one central question has loomed since Plath’s death: What role did Hughes play, intentionally or not, in her death? “Red Comet” reports what Hughes said on the matter. “No doubt where the blame lies,” Hughes wrote to a friend. “It doesn’t fall to many men to murder a genius,” Hughes said to Plath’s friend Elizabeth Compton, adding on another occasion, “I feel like a murderer.” To Aurelia Plath, Hughes wrote: “[I]f there is an eternity, I am damned in it. Sylvia was one of the greatest truest spirits alive.”

In a letter to the Observer newspaper (never mailed) that was meant to thank Plath’s friends and neighbors, Aurelia seemed to concur: “Those who systematically and deliberately destroyed her know who they are.”

Plath’s loss continues to resonate. “With each passing decade,” Clark concludes, “Sylvia Plath’s work seems more astonishing, and its achievements harder earned. . . . Let us not desert her.”

Paul Alexander is the author of “Rough Magic,” a biography of Sylvia Plath, and “Edge,” a one-woman play about her. The editor of “Ariel Ascending: Writings About Sylvia Plath,” he teaches at Fordham University and Hunter College.

Red Comet
The Short Life and Blazing Art of Sylvia Plath
By Heather Clark
Knopf. 1,118 pp. $40