Plath was born on October 27, 1932, in the Massachusetts Memorial Hospital, in Boston’s Jamaica Plain neighborhood. Her mother, Aurelia Schober Plath (1906–1994), was a first-generation American of Austrian descent, and her father, Otto Plath (1885–1940), was from Grabow, Germany. Plath’s father was an entomologist and was a professor of biology at Boston University; he also authored a book about bumblebees. Plath’s mother was approximately 21 years younger than her husband.  On April 27, 1935, Plath’s brother Warren was born and in 1936 the family moved from 24 Prince Street in Jamaica Plain, Massachusetts, to 92 Johnson Avenue, Winthrop, Massachusetts. Plath’s mother, Aurelia, had grown up in Winthrop, and her maternal grandparents, the Schobers, had lived in a section of the town called Point Shirley, a location mentioned in Plath’s poetry. While living in Winthrop, eight-year-old Plath published her first poem in the Boston Herald’s children’s section. In addition to writing, she showed early promise as an artist, winning an award for her paintings from The Scholastic Art & Writing Awards in 1947.

Otto Plath died on November 5, 1940, a week and a half after Plath’s eighth birthday, of complications following the amputation of a foot due to untreated diabetes. He had become ill shortly after a close friend died of lung cancer. Comparing the similarities between his friend’s symptoms and his own, Otto became convinced that he, too, had lung cancer and did not seek treatment until his diabetes had progressed too far. Raised as a Unitarian Christian, Plath experienced a loss of faith after her father’s death, and remained ambivalent about religion throughout her life. He was buried in Winthrop Cemetery; visiting her father’s grave prompted Plath to write the poem Electra on Azalea Path. After his death, Aurelia Plath moved her children and her parents to 26 Elmwood Road, Wellesley, Massachusetts in 1942. In one of her last prose pieces, Plath commented that her first nine years “sealed themselves off like a ship in a bottle—beautiful inaccessible, obsolete, a fine, white flying myth”. Plath attended Bradford Senior High School (now Wellesley High School) in Wellesley, graduating in 1950.

In 1950, Plath attended Smith College and excelled academically. She wrote to her mother, “The world is splitting open at my feet like a ripe, juicy watermelon.” She edited The Smith Review and during the summer after her third year of college was awarded a coveted position as guest editor at Mademoiselle magazine, during which she spent a month in New York City. The experience was not what she had hoped it would be, and it began a downward spiral. She was furious at not being at a meeting the editor had arranged with Welsh poet Dylan Thomas—a writer whom she loved, said one of her boyfriends, “more than life itself.” She hung around the White Horse bar and the Chelsea Hotel for two days hoping to meet Thomas, but he was already on his way home. A few weeks later she was to slash her legs to see if she had enough courage to commit suicide. Many of the events that took place during that summer were later used as inspiration for her novel The Bell Jar. During this time she was refused admission to the Harvard writing seminar. Following electroconvulsive therapy for depression, Plath made her first medically documented suicide attempt in late August 1953 by crawling under her house and taking her mother’s sleeping pills.

She survived this first suicide attempt after lying unfound in a crawl space for three days, later writing that she “blissfully succumbed to the whirling blackness that I honestly believed was eternal oblivion.” She spent the next six months in psychiatric care, receiving more electric and insulin shock treatment under the care of Dr. Ruth Beuscher. Her stay at McLean Hospital and her Smith scholarship were paid for by Olive Higgins Prouty, who had successfully recovered from a mental breakdown herself. Plath seemed to make a good recovery and returned to college. In January 1955, she submitted her thesis The Magic Mirror: A Study of the Double in Two of Dostoyevsky’s Novels and in June, graduated from Smith with highest honors.  She obtained a Fulbright scholarship to study at Newnham College, one of the three women-only colleges of Cambridge University in England, where she continued actively writing poetry and publishing her work in the student newspaper Varsity. At Newnham, she studied with Dorothea Krook, whom she held in high regard. She spent her first year winter and spring holidays traveling around Europe.

Plath first met poet Ted Hughes on February 25, 1956, at a party in Cambridge.  Plath described Hughes as “a singer, story-teller, lion and world-wanderer” with “a voice like the thunder of God”.  The couple married on June 16, 1956, at St George the Martyr Holborn in the London Borough of Camden with Plath’s mother in attendance, and spent their honeymoon in Benidorm. Plath returned to Newnham in October to begin her second year. During this time, they both became deeply interested in astrology and the supernatural, using Ouija boards. In early 1957, Plath and Hughes moved to the United States and from September 1957 Plath taught at Smith College, her alma mater. She found it difficult to both teach and have enough time and energy to write and in the middle of 1958, the couple moved to Boston. Plath took a job as a receptionist in the psychiatric unit of Massachusetts General Hospital and in the evening took creative writing seminars given by poet Robert Lowell (also attended by the writers Anne Sexton and George Starbuck). Both Lowell and Sexton encouraged Plath to write from her experience and she did so. She openly discussed her depression with Lowell and her suicide attempts with Sexton, who led her to write from a more female perspective. Plath began to conceive of herself as a more serious, focused poet and short-story writer. At this time Plath and Hughes first met the poet W. S. Merwin, who admired their work and was to remain a lifelong friend. Plath resumed psychoanalytic treatment in December, working with Ruth Beuscher.

Plath and Hughes traveled across Canada and the United States, staying at the Yaddo artist colony in Saratoga Springs, New York State in late 1959. Plath says that it was here that she learned “to be true to my own weirdnesses,” but she remained anxious about writing confessionally, from deeply personal and private material. The couple moved back to the United Kingdom in December 1959 and lived in London at 3 Chalcot Square, near the Primrose Hill area of Regent’s Park, where an English Heritage plaque records Plath’s residence. Their daughter Frieda was born on April 1, 1960 and in October, Plath published her first collection of poetry, The Colossus. In February 1961, Plath’s second pregnancy ended in miscarriage; several of her poems, including “Parliament Hill Fields”, address this event. In August she finished her semi-autobiographical novel The Bell Jar and immediately after this, the family moved to Court Green in the small market town of North Tawton in Devon. Nicholas was born in January 1962. In mid-1962, Hughes began to keep bees, which would be the subject of many Plath poems.

In 1961, the couple rented their flat at Chalcot Square to Assia and David Wevill. Hughes was immediately struck with the beautiful Assia, as she was with him. In June 1962, Plath had had a car accident which she described as one of many suicide attempts. In July 1962, Plath discovered Hughes had been having an affair with Assia Wevill and in September the couple separated.  Beginning in October 1962, Plath experienced a great burst of creativity and wrote most of the poems on which her reputation now rests, writing at least 26 of the poems of her posthumous collection Ariel during the final months of her life. In December 1962, she returned alone to London with their children, and rented, on a five-year lease, a flat at 23 Fitzroy Road—only a few streets from the Chalcot Square flat. William Butler Yeats once lived in the house, which bears an English Heritage blue plaque for the Irish poet. Plath was pleased by this fact and considered it a good omen.  The northern winter of 1962–3 was one of the coldest in 100 years; the pipes froze, the children—now two years old and nine months—were often sick, and the house had no telephone. Her depression returned but she completed the rest of her poetry collection which would be published after her death (1965 in the UK, 1966 in the US). Her only novel, The Bell Jar, came out in January 1963, published under the pen name Victoria Lucas, and was met with critical indifference.

Dr. John Horder, a close friend who lived near Plath, prescribed her antidepressants a few days before her suicide. Knowing she was at risk alone with two young children, he says he visited her daily and made strenuous efforts to have her admitted to a hospital; when that failed, he arranged for a live-in nurse. Commentators have argued that because antidepressants may take up to three weeks to take effect, her prescription from Horder would not have taken full effect.  The nurse was due to arrive at 9:00 the morning of February 11, 1963 to help Plath with the care of her children. Upon arrival, she could not get into the flat, but eventually gained access with the help of a workman, Charles Langridge. They found Plath dead of carbon monoxide poisoning in the kitchen, with her head in the oven, having sealed the rooms between herself and her sleeping children with wet towels and cloths. At approximately 4:30 am, Plath had placed her head in the oven, with the gas turned on. She was 30 years old.

Some have suggested that Plath had not intended to kill herself. That morning, she asked her downstairs neighbor, a Mr. Thomas, what time he would be leaving. She also left a note reading “Call Dr. Horder,” including the doctor’s phone number. Therefore, it is argued Plath turned on the gas at a time when Mr. Thomas would have been able to see the note. However, in her biography Giving Up: The Last Days of Sylvia Plath, Plath’s best friend, Jillian Becker wrote, “According to Mr. Goodchild, a police officer attached to the coroner’s office … [Plath] had thrust her head far into the gas oven… [and] had really meant to die.” Dr. Horder also believed her intention was clear. He stated that “No one who saw the care with which the kitchen was prepared could have interpreted her action as anything but an irrational compulsion.” Plath had described the quality of her despair as “owl’s talons clenching my heart.” In his 1971 book on suicide, friend and critic Al Alvarez claimed that Plath’s suicide was an unanswered cry for help.