King was born September 21, 1947, in Portland, Maine. His father, Donald Edwin King, was a merchant seaman. Donald was born under the surname Pollock, but as an adult, used the surname King. King's mother was Nellie Ruth (née Pillsbury).

King attended Durham Elementary School and graduated from Lisbon Falls High School, in Lisbon Falls, Maine. He displayed an early interest in horror as an avid reader of EC's horror comics, including Tales from the Crypt (he later paid tribute to the comics in his screenplay for Creepshow). He began writing for fun while still in school, contributing articles to Dave's Rag, the newspaper his brother published with a mimeograph machine, and later began selling to his friends stories based on movies he had seen (though when discovered by his teachers, he was forced to return the profits). The first of his stories to be independently published was "I Was a Teenage Grave Robber"; it was serialized over four issues (three published and one unpublished) of a fanzine, Comics Review, in 1965. That story was published the following year in a revised form as "In a Half-World of Terror" in another fanzine, Stories of Suspense, edited by Marv Wolfman. As a teen, King also won a Scholastic Art and Writing Award.

From 1966, King studied at the University of Maine, graduating in 1970 with a Bachelor of Arts in English. That year, his daughter Naomi Rachel was born. He wrote a column, Steve King's Garbage Truck, for the student newspaper, The Maine Campus and participated in a writing workshop organized by Burton Hatlen. King held a variety of jobs to pay for his studies, including janitor, gas pump attendant, and worker at an industrial laundry.

King sold his first professional short story, "The Glass Floor", to Startling Mystery Stories in 1967. The Fogler Library at the University of Maine now holds many of King's papers.

In the late 1970s and early 1980s, King published a handful of short novels—Rage (1977), The Long Walk (1979), Roadwork (1981), The Running Man (1982) and Thinner (1984)—under the pseudonym Richard Bachman. The idea behind this was to test whether he could replicate his success again and to allay his fears that his popularity was an accident. An alternate explanation was that publishing standards at the time allowed only a single book a year. He picked up the name from the hard rock band Bachman-Turner Overdrive, of which he is a fan.

King married Tabitha Spruce in 1971. She too is a Novelist and philanthropic Activist. The couple own and occupy three different houses: one in Bangor, Maine, one in Lovell, Maine, and for the winter a waterfront mansion located off the Gulf of Mexico in Sarasota, Florida. The Kings have three children, a girl and two boys, and four grandchildren. Their daughter Naomi is a Unitarian Universalist Church minister in Plantation, Florida, with her same-sex partner, Rev. Dr. Thandeka. Both of the Kings' sons are authors: Owen King published his first collection of stories, We're All in This Together: A Novella and Stories, in 2005. Joseph Hillstrom King, who writes as Joe Hill, published a collection of short stories, 20th Century Ghosts, in 2005. His debut novel, Heart-Shaped Box (2007), was optioned by Warners Bros.

King has used other pseudonyms. The short story "The Fifth Quarter" was published under the pseudonym John Swithen (the name of a character in the novel Carrie), that was published in Cavalier in April 1972. The story was later reprinted in King's collection Nightmares & Dreamscapes in 1993 under his own name. In the introduction to the Bachman novel Blaze, King claims, with tongue-in-cheek, that "Bachman" was the person using the Swithen pseudonym.

In 1973, King's first novel Carrie was accepted by publishing house Doubleday. King had thrown an early draft of the novel into the trash after becoming discouraged with his progress writing about a teenage girl with psychic powers. His wife retrieved the manuscript and encouraged him to finish it. His advance for Carrie was $2,500; King's paperback rights later earned $400,000.

King and his family moved to southern Maine because of his mother's failing health. At this time, he began writing a book titled Second Coming, later titled Jerusalem's Lot, before finally changing the title to 'Salem's Lot (published 1975). In a 1987 issue of The Highway Patrolman magazine, he stated, "The story seems sort of down home to me. I have a special cold spot in my heart for it!" Soon after Carrie's release in 1974, King's mother died of uterine cancer. His Aunt Emrine had read the novel to her before she died. King has written of his severe drinking Problem at this time, stating that he was drunk delivering the eulogy at his mother's funeral.

After his mother's death, King and his family moved to Boulder, Colorado, where King wrote The Shining (published 1977). The family returned to western Maine in 1975, where King completed his fourth novel, The Stand (published 1978). In 1977, the family, with the addition of Owen Phillip (his third and last child), traveled briefly to England, returning to Maine that fall, where King began teaching creative writing at the University of Maine. He has kept his primary residence in Maine ever since.

King's addictions to alcohol and other drugs were so serious during the 1980s that, as he acknowledged in On Writing in 2000, he can barely remember writing Cujo. Shortly after the novel's publication, King's family and friends staged an intervention, dumping on the rug in front of him evidence of his addictions taken from his office including beer cans, cigarette butts, grams of cocaine, Xanax, Valium, NyQuil, dextromethorphan (cough medicine) and marijuana. As King related in his memoir, he then sought help, quit all drugs (including alcohol) in the late 1980s, and has remained sober since. The first novel he wrote after becoming sober was Needful Things.

King related in detail his primary inspiration for writing horror fiction in his non-fiction Danse Macabre (1981), in a chapter titled "An Annoying Autobiographical Pause". King compares his uncle's dowsing for water using the bough of an apple branch with the sudden realization of what he wanted to do for a living. That inspiration occurred while browsing through an attic with his elder brother, when King uncovered a paperback version of an H. P. Lovecraft collection of short stories he remembers as The Lurker in the Shadows, that had belonged to his father. King told Barnes & Noble Studios during a 2009 interview, "I knew that I'd found home when I read that book."

King has written two novels with horror Novelist Peter Straub: The Talisman (1984) and a sequel, Black House (2001). King has indicated that he and Straub will likely write the third and concluding book in this series, the tale of Jack Sawyer, but has set no time for its completion.

King's first film appearance was in George Romero's Knightriders as a buffoonish audience member. His first featured role was in Creepshow, in particular the segment "The Lonesome Death of Jordy Verrill" (King also having written the original story), where he plays the titular character. He has since made cameos in several adaptations of his works. He appeared in Pet Sematary as a minister at a funeral, in Thinner as a pharmacist, in Rose Red as a pizza deliveryman, as a news reporter in The Storm of the Century, in The Stand as "Teddy Wieszack," in the Shining miniseries as a band member, in The Langoliers as Tom Holby; in Sleepwalkers as the cemetery caretaker and Golden Years as a bus driver. He has also appeared in Chappelle's Show and, along with fellow author Amy Tan, on The Simpsons as himself. In addition to acting, King tried his hand at directing with Maximum Overdrive, in which he also made a cameo appearance as a man using a malfunctioning ATM. King had also been approached to appear in the 1985 Romero film Day of the Dead as a zombie. Although King declined due to scheduling conflicts, a copy of one of his works makes an appearance being held by the foremost zombie "Bub". King would once again work with Romero in 1993 when his work The Dark Half was filmed and directed by George Romero.

King is also a fan of hard rock such as AC/DC; he arranged for their album Who Made Who to feature as the score for the film he directed in 1986, Maximum Overdrive. King has also stated that he likes heavy metal and has named bands like Anthrax, Judas Priest and Metallica as amongst his favourites to write to. In 1988, the band Blue Öyster Cult recorded an updated version of its 1974 song "Astronomy". The single released for radio play featured a narrative intro spoken by King. The Blue Öyster Cult song "(Don't Fear) The Reaper" was also used in the King TV series The Stand.

In 1987, King's Philtrum Press published Don Robertson's novel The Ideal, Genuine Man. In his forenote to the novel, King wrote, "Don Robertson was and is one of the three Writers who influenced me as a young man who was trying to 'become' a Novelist (the other two being Richard Matheson and John D. MacDonald)." Robert A. Heinlein's book The Door into Summer is repeatedly mentioned in King's Wolves of the Calla (2003), as are several other works. Wolves of the Calla is the King work in which The Dark Tower begins to follow a meta-fictional path.

King is a fan of baseball, and of the Boston Red Sox in particular; he frequently attends the team's home and away games, and occasionally mentions the team in his novels and stories. He helped coach his son Owen's Bangor West team to the Maine Little League Championship in 1989. He recounts this experience in the New Yorker essay "Head Down", which appears also in the collection Nightmares & Dreamscapes. In 1999, King wrote The Girl Who Loved Tom Gordon, featuring former Red Sox pitcher Tom Gordon as the protagonist's imaginary companion. In 2004, King co-wrote a book titled Faithful: Two Diehard Boston Red Sox Fans Chronicle the Historic 2004 Season with Stewart O'Nan, recounting the authors' roller-coaster reaction to the Red Sox's 2004 season, a season culminating in the Sox winning the 2004 American League Championship Series and World Series. In the 2005 film Fever Pitch, about an obsessive Boston Red Sox fan, King tosses out the first pitch of the Sox's opening-day game.

In his book The Philosophy of Horror (1990), Noël Carroll discusses King's work as an exemplar of modern horror fiction. Analyzing both the narrative structure of King's fiction and King's non-fiction ruminations on the art and craft of writing, Carroll writes that for King, "the horror story is always a contest between the normal and the abnormal such that the normal is reinstated and, therefore, affirmed."

King made an appearance as a contestant on Celebrity Jeopardy! in 1995, playing to benefit the Bangor Public Library.

In 1996, King won an O. Henry Award for his short story "The Man in the Black Suit".

On June 19, 1999, at about 4:30 p.m., King was walking on the shoulder of Maine State Route 5, in Lovell, Maine. Driver Bryan Edwin Smith, distracted by an unrestrained dog moving in the back of his minivan, struck King, who landed in a depression in the ground about 14 feet (4 meters) from the pavement of Route 5. According to Oxford County Sheriff deputy Matt Baker, King was hit from behind and some witnesses said the driver was not speeding, reckless, or drinking. In his book On Writing King states he was heading north, walking against the traffic. Shortly before the accident took place, a woman in a car also heading north passed first King and then the light blue Dodge van. The van was looping from one side of the road to the other and the woman told her Passenger she hoped "that guy in the van doesn't hit him".

King's formula for learning to write well is: "Read and write four to six hours a day. If you cannot find the time for that, you can't expect to become a good Writer." He sets out each day with a quota of 2000 words and will not stop writing until it is met. He also has a simple definition for talent in writing: "If you wrote something for which someone sent you a check, if you cashed the check and it didn't bounce, and if you then paid the light bill with the money, I consider you talented."

The Diary of Ellen Rimbauer: My Life at Rose Red (2001) was a paperback tie-in for the King-penned miniseries Rose Red (2002). Published under anonymous authorship, the book was written by Ridley Pearson. The novel is written in the form of a diary by Ellen Rimbauer, and annotated by the fictional professor of paranormal activity, Joyce Reardon. The novel also presents a fictional afterword by Ellen Rimbauer's grandson, Steven. Intended to be a promotional item rather than a stand-alone work, its popularity spawned a 2003 prequel television miniseries to Rose Red, titled The Diary of Ellen Rimbauer. This spin-off is a rare occasion of another author's being granted permission to write commercial work using characters and story elements invented by King. The novel tie-in idea was repeated on Stephen King's next project, the miniseries Kingdom Hospital. Richard Dooling, King's collaborator on Kingdom Hospital and Writer of several episodes in the miniseries, published a fictional diary, The Journals of Eleanor Druse, in 2004. Eleanor Druse is a key character in Kingdom Hospital, much as Dr. Joyce Readon and Ellen Rimbauer are key characters in Rose Red.

In 2002, King announced he would stop writing, apparently motivated in part by frustration with his injuries, which had made sitting uncomfortable and reduced his stamina. He has since resumed writing, but states on his website:

In 2003, King was honored by the National Book Awards with a lifetime achievement award, the Medal of Distinguished Contribution to American Letters. Some in the literary community expressed disapproval of the award: Richard E. Snyder, the former CEO of Simon & Schuster, described King's work as "non-literature", and critic Harold Bloom denounced the choice:

In Roger Ebert's review of the 2004 movie Secret Window, he stated, "A lot of people were outraged that [King] was honored at the National Book Awards, as if a popular Writer could not be taken seriously. But after finding that his book On Writing had more useful and observant things to say about the craft than any book since Strunk and White's The Elements of Style, I have gotten over my own snobbery."

During this time, Tabitha King was inspired to redesign his studio. King visited the space while his books and belongings were packed away. What he saw was an image of what his studio would look like if he died, providing a seed for his novel Lisey's Story (2006).

In 2006, during a press conference in London, King declared that he had discovered another Bachman novel, titled Blaze. It was published on June 12, 2007. In fact, the original manuscript had been held at King's alma mater, the University of Maine in Orono, for many years and had been covered by numerous King experts. King rewrote the original 1973 manuscript for its publication.

King's website states that he is a supporter of the Democratic Party. During the 2008 presidential election, King voiced his support for Democratic candidate Barack Obama. King was quoted as calling conservative commentator Glenn Beck "Satan's mentally challenged younger brother."

In an interview with King, published in the USA Weekend in March 2009, the author stated, "People look on Writers that they like as an irreplaceable resource. I do. Elmore Leonard, every day I wake up and—not to be morbid or anything, although morbid is my life to a degree—don't see his obituary in the paper, I think to myself, "Great! He's probably working somewhere. He's gonna produce another book, and I'll have another book to read. Because when he's gone, there's nobody else."

In 2010, King appeared in a cameo role as a cleaner named Bachman (a reference to his pen name Richard Bachman) on the FX series Sons of Anarchy.

In November 2011, the STK Foundation donated $70,000 in matched funding via his radio station to help pay the heating bills for families in need in his home town of Bangor, Maine, during the winter.

On April 30, 2012, King published an article in The Daily Beast calling for rich Americans, including himself, to pay more taxes, citing it as "a practical necessity and moral imperative that those who have received much should be obligated to pay ... in the same proportion".

On January 25, 2013, King published an essay titled "Guns" via Amazon.com's Kindle single feature, which discusses the gun debate in the wake of the Sandy Hook Elementary School shooting. King called for gun owners to support a ban on automatic and semi-automatic weapons, writing, "Autos and semi-autos are weapons of mass destruction...When lunatics want to make war on the unarmed and unprepared, these are the weapons they use." The essay became the fifth-bestselling non-fiction title for the Kindle.

King had endorsed Shenna Bellows in the 2014 U.S. Senate election for the seat held by Republican Susan Collins.

King sent a tweet on June 30, 2015, stating that LePage is "a terrible embarrassment to the state I live in and love. If he won't govern, he should resign." He later clarified that he was not calling on LePage to resign, but to "go to work or go back home". On August 27, 2016, King sent another tweet about LePage, calling him "a bigot, a homophobe, and a racist".

The "children's book" Charlie the Choo-Choo: From the World of The Dark Tower was published under the pseudonym Beryl Evans, who was portrayed by Actress Allison Davies during a book signing at San Diego Comic-Con, and illustrated by Ned Dameron. It is adapted from a fictional book central to the plot of King's previous novel The Dark Tower III: The Waste Lands and published in 2016.

King and his son Owen King co-wrote the novel Sleeping Beauties, released in 2017, that is set in a women's prison.

The attention garnered by the LePage criticism has led to efforts to encourage King to run for Governor of Maine in 2018. Bangor city councilor Joe Baldacci posted on his Facebook page that he was starting a Draft Stephen King effort, and Democratic State Rep. Diane Russell launched a petition drive to encourage King to run. His spokeswoman posted to Baldacci's Facebook comment that he would likely decline to run, and King himself stated he would not run or serve on March 23 while still criticizing what he said was the "laziness that made him mad" about not checking his tax payments and that LePage had "a Problem finding a comfortable pair of big-boy pants".