Howard was born January 22, 1906 in Peaster, Texas, the only son of a traveling country physician, Dr. Isaac Mordecai Howard, and his wife, Hester Jane Ervin Howard. His early life was spent wandering through a variety of Texas cowtowns and boomtowns: Dark Valley (1906), Seminole (1908), Bronte (1909), Poteet (1910), Oran (1912), Wichita Falls (1913), Bagwell (1913), Cross Cut (1915), and Burkett (1917).

Voracious reading, along with a natural talent for prose writing and the encouragement of teachers, created in Howard an interest in becoming a professional Writer. From the age of nine he began writing stories, mostly tales of historical fiction centering on Vikings, Arabs, battles, and bloodshed. One by one he discovered the authors who would influence his later work: Jack London and his stories of reincarnation and past lives, most notably The Star Rover (1915); Rudyard Kipling's tales of subcontinent adventure and his chanting, shamanic verse; the classic mythological tales collected by Thomas Bulfinch. Howard was considered by friends to be eidetic, and astounded them with his ability to memorize lengthy reams of poetry with ease after one or two readings.

In 1919, when Howard was thirteen, Dr. Howard moved his family to the Central Texas hamlet of Cross Plains, and there the family would stay for the rest of Howard's life. Howard's father bought a house in the town with a cash down payment and made extensive renovations. That same year, sitting in a library in New Orleans while his father took medical courses at a nearby college, Howard discovered a book concerned with the scant fact and abundant legends surrounding an indigenous culture in ancient Scotland called the Picts.

In 1920, on February 17, the Vestal Well within the limits of Cross Plains struck oil and Cross Plains became an oil boomtown. Thousands of people arrived in the town looking for oil wealth. New businesses sprang up from scratch and the crime rate increased to match. Cross Plains' population quickly grew from 1,500 to 10,000, it suffered overcrowding, the traffic ruined its unpaved roads and vice crime exploded but it also used its new wealth on civic improvements, including a new school, an ice Manufacturing plant, and new hotels. Howard hated the boom and despised the people who came with it. He was already poorly disposed towards oil booms as they were the cause of the constant traveling in his early years but this was aggravated by what he perceived to be the effect oil booms had on towns.

In the fall of 1922, when Howard was sixteen, he temporarily moved to a boarding house in the nearby city of Brownwood to complete his senior year of high school, accompanied by his mother. It was in Brownwood that he first met friends his own age who shared his interest not only for Sports and history but also writing and poetry. The two most important of these, Tevis Clyde Smith and Truett Vinson, shared his Bohemian and literary outlook on life, and together they wrote amateur papers and magazines, exchanged long letters filled with poetry and existential thoughts on life and philosophy, and encouraged each other's writing endeavors. Through Vinson, Howard was introduced to The Tattler, the newspaper of the Brownwood High School. It was in this publication that Howard's stories were first printed. The December 1922 issue featured two stories, "'Golden Hope Christmas" and "West is West," which won gold and silver prizes respectively.

Howard's first published poem was The Sea, in an early 1923 issue of local newspaper The Baylor United Statement. His first published story was "Spear and Fang", sold in late November 1924 and published in the July 1925 issue of the pulp magazine Weird Tales. However, Howard's first real success was the Sailor Steve Costigan series of humorous boxing stories, beginning with "The Pit of the Serpent" published in the July 1929 issue of the pulp magazine Fight Stories.

Howard spent his late teens working odd jobs around Cross Plains, all of which he hated. In 1924, Howard returned to Brownwood to take a stenography course at Howard Payne College, this time boarding with his friend Lindsey Tyson instead of his mother. Howard would have preferred a literary course but was not allowed to take one for some reason. Biographer Mark Finn suggests that his father refused to pay for such a non-vocational education. In the week of Thanksgiving that year, and after years of rejection slips and near acceptances, he finally sold a short caveman tale titled "Spear and Fang", which netted him the sum of $16 and introduced him to the readers of a struggling pulp called Weird Tales.

Weird Tales paid on publication, meaning that Howard had no money of his own at this time. To remedy this, he took a job writing oil news for the local newspaper Cross Plains Review at $5 per column. It was not until July 1925 that Howard received payment for his first printed story. Howard lost his job at the newspaper in the same year and spent one month working in a post office before quitting over the low wages. His next job, at the Cross Plains Natural Gas Company, did not last long due to his refusal to be subservient to his boss. He did manual labor for a surveyor for a time before beginning a job as a stenographer for an oil company.

In August 1926, Howard quit his exhausting job at the drug store and, in September, returned to Brownwood to complete his bookkeeping course. It was during this August that he began working on the story that would become "The Shadow Kingdom", one of the most important works of his career. While at college, Howard wrote for their newspaper, The Yellow Jacket. One of the short stories printed in this newspaper was a comedy called "Cupid vs. Pollux." This story is Howard's earliest surviving boxing story known to exist; it is told in the first person, uses elements of a traditional tall-tale and is a fictionalized account of Howard (as "Steve") and his friend Lindsey Tyson (as "Spike") training for a fight. This story and the elements it uses would also be important in Howard's literary Future.

In May 1927, after having to return home due to contracting measles and then being forced to retake the course, Howard passed his exams. While waiting for the official graduation in August, he returned to writing, including a re-write of "The Shadow Kingdom." He rewrote it again in August and submitted it to Weird Tales in September. This story was an experiment with the entire concept of the "weird tale" horror fiction as defined by practitioners such as Edgar Allan Poe, A. Merritt, and H. P. Lovecraft; mixing elements of fantasy, horror and mythology with historical romance, action and swordplay into thematic vehicles never before seen, a new style of tale which ultimately became known as "sword and sorcery". Featuring Kull, a barbarian precursor to later Howard heroes such as Conan, the tale hit Weird Tales in August 1929 and received fanfare from readers. Weird Tales Editor Farnsworth Wright bought the story for $100, the most Howard had earned for a story at this time, and several more Kull stories followed. However, all but two were rejected, convincing Howard not to continue the series.

In March 1928, Howard salvaged and re-submitted to Weird Tales a story rejected by the more popular pulp Argosy, and the result was "Red Shadows", the first of many stories featuring the vengeful Puritan swashbuckler Solomon Kane. Appearing in the August 1928 issue of Weird Tales, the character was a big hit with readers and this was the first of Howard's characters to sustain a series in print beyond just two stories (seven Kane stories were printed in the 1928–32 period). As the magazine published the Solomon Kane tale before Kull, this can be considered the first published Example of sword and sorcery.

After several minor successes and false starts, he struck gold again with a new series based on one of his favorite passions: boxing. July 1929 saw the debut of Sailor Steve Costigan in the pages of Fight Stories. A tough-as-nails, two-fisted mariner with a head of rocks and occasionally a heart of gold, Costigan began boxing his way through a variety of exotic seaports and adventure locales, becoming so popular in Fight Stories that the same editors began using additional Costigan episodes in their sister magazine Action Stories. The series saw a return to Howard's use of humor and (unreliable) first-person narration, with the combination of a traditional tall tale and slapstick comedy. Stories sold to Fight Stories provided Howard with a market just as stable as Weird Tales.

In 1930, with his interest in Solomon Kane dwindling and his Kull stories not catching on, Howard applied his new sword-and-sorcery and horror experience to one of his first loves: the Picts. His story "Kings of the Night" depicted King Kull conjured into pre-Christian Britain to aid the Picts in their struggle against the invading Romans, and introduced readers to Howard's king of the Picts, Bran Mak Morn. Howard followed up this tale with the now-classic revenge nightmare "Worms of the Earth" and several other tales, creating horrific adventures tinged with a Cthulhu-esque gloss and notable for their memorable use of metaphor and symbolism.

Howard was both influenced by and an influence on his friend H. P Lovecraft. Many ideas that he discussed in his letters to Lovecraft were repeated in his fiction and the discussion with a fellow professional Writer was useful to him. For his part, Lovecraft began to include Howardian action sequences in his own work, for Example in "The Shadow Over Innsmouth". Much of 1931 was spent by Howard attempting to mimic Lovecraft's style. After that year, he had absorbed the parts of it that worked best for him and made them his own.

After Howard bought a car in 1932, he and his friends took regular excursions across Texas and nearby states. His letters to Lovecraft also contain information about the history and geography he encountered on his journeys. Howard was also a practitioner and fan of boxing, as well as an avid Weight Lifter.

Howard is only known to have had one girlfriend in his life, Novalyne Price. Price was an ex-girlfriend of Tevis Clyde Smith, one of Howard's best friends, whom she had known since high school and they had remained friends after their relationship ended. She first met Howard in spring 1933 when Howard was visiting Smith after driving his mother to a Brownwood clinic. Howard and Smith drove to the Price farm and Smith introduced his friends to each other. Price was an aspiring Writer, had heard of Howard from Smith in the past and was enthusiastic to meet him in person. However, he was not what she expected. She wrote in her diary about this first meeting: "This man was a Writer! Him? It was unbelievable. He was not dressed as I thought a Writer should dress." They parted after a drive and would not see each other again for over a year.

Physically, Howard was tall and heavily built. He had a gentle, round face with a soft, deep voice. E. Hoffmann Price wrote that when he first met Howard in 1934 he "was busy trying to combine two images, that of the actual man, and that of the man who loomed up in those stirring yarns. The synthesis was never effected. He was packed with the whimsy and poetry which rang out in his letters, and blazed up in much of his published fiction, but, as is usually the case with Writers, his appearance belied him. His face was boyish, not yet having squared off into angles; his blue eyes slightly prominent, had a wide-openness which did not suggest anything of the man's keen wit and agile fancy. That first picture persists—a powerful, solid, round-faced fellow, kindly and somewhat stolid seeming."

In hindsight, there were hints about Howard's plans. Several times in 1935–36, whenever his mother's health had precipitously threatened to give out, he made veiled allusions to his father about planning suicide, which his father did not understand at the time. He had made references when speaking to Novalyne Price about her being in his "sere and yellow leaf." The words sounded familiar to her, but it was only in early June 1936 that she found the source in Macbeth:

Robert E. Howard's legacy extended after his death in 1936. Howard's most famous character, Conan the Barbarian, has a pop-culture imprint that has been compared to such icons as Tarzan of the Apes, Count Dracula, Sherlock Holmes, and James Bond. Howard's critical reputation suffered at first but over the decades works of Howard scholarship have been published. The first professionally published Example of this was L. Sprague de Camp's Dark Valley Destiny (1983) which was followed by other works, including Don Herron's The Dark Barbarian (1984) and Mark Finn's Blood & Thunder (2006). Also in 2006, a charity, Robert E. Howard Foundation, was created to promote further scholarship.

Howard's first published novel, A Gent from Bear Creek, was printed in Britain one year after his death. This was followed in the United States by a collection of Howard's stories, Skull-Face and Others (1946) and then the novel Conan the Conqueror (1950). The success of Conan the Conqueror led to a series of Conan books from publisher Gnome Press, the later Editor of which was L. Sprague de Camp. The series led to the first Conan pastiche, the novel The Return of Conan by de Camp and Swedish Howard fan Björn Nyberg. De Camp eventually achieved control over the Conan stories and Conan brand in general. Oscar Friend took over from Kline as literary agent and he was followed by his daughter Kittie West. When she closed the agency in 1965, a new agent was required. De Camp was offered the role but he recommended Glenn Lord instead. Lord began as a fan of Howard and had re-discovered many unpublished pieces that would otherwise have been lost, printing them in books such as Always Comes Evening (1957) and his own magazine The Howard Collector (1961–1973). He became responsible for the non-Conan works and later restored, textually-pure versions of the Conan stories themselves.

In 1966, de Camp made a deal with Lancer Books to republish the Conan series, which led to the "First Howard Boom" of the 1970s; their popularity was enhanced by the cover artwork of Frank Frazetta on most of the volumes. Many of his works were reprinted (some printed for the first time) and they expanded into other media such as comic books and films. The Conan stories were increasingly edited by de Camp and the series was extended by pastiches until they replaced the original stories. In response, a puristic movement grew up demanding Howard's original, un-edited stories. The first boom ended in the mid-1980s. In the late 1990s and early 21st century, the "Second Howard Boom" occurred. This saw the printing of new collections of Howard's work, with the restored texts desired by purists. As before, the boom led to new comic books, films and computer games. Howard's house in Cross Plains has been converted into the Robert E. Howard Museum, which has been added to the National Register of Historic Places.

The works of Robert E. Howard have been adapted into multiple media, such as the two Conan films released in the 1980s starring Arnold Schwarzenegger. In addition to the Conan films, other adaptations have included Kull the Conqueror (1997) and Solomon Kane (2009). In television, the anthology series Thriller (1961) led the adaptations with an episode based on the short story "Pigeons from Hell." The bulk of the adaptations have, however, been based on Conan with two animated and one live action series. Multiple audio dramas have been adapted, from professional audio books and plays to LibriVox recordings of works in the public domain. Computer games have focussed on Conan, beginning with Conan: Hall of Volta (1984) and continuing on to the MMO Age of Conan: Hyborian Adventures (2008). The first table-top roleplaying game based on Howard's works was TSR's "Conan Unchained!" (1984) for their game Advanced Dungeons & Dragons. The first comic book adaptation was in the Mexican Cuentos de Abuelito – La Reina de la Costa Negra No. 17 (1952). Howard related comic books continued to be published to the present day. Howard is an ongoing inspiration for and influence on heavy metal music. Several bands have adapted Howard's works to tracks or entire albums. The British metal band Bal-Sagoth is named after Howard's story "The Gods of Bal-Sagoth."

Three publishing houses have put out collections of Howard's letters. In 1989 and 1991, Necronomicon Press published Robert E. Howard: Selected Letters in two volumes (1923–1930 and 1931–1936) edited by Glenn Lord with Rusty Burke, S. T. Joshi, and Steve Behrends. In 2007 and 2008, The Robert E. Howard Foundation Press published a three volume set (1923–1929, 1930–1932, and 1933–1936) titled The Collected Letters of Robert E. Howard, edited by Rob Roehm. Additionally, in 2009, Hippocampus Press published two volumes (1930–1932 and 1933–1936) of Howard's correspondence with H. P. Lovecraft as A Means to Freedom: The Letters of H.P. Lovecraft & Robert E. Howard, edited by S. T. Joshi, David Schultz, and Rusty Burke.

In an effort to improve her memory and writing, Price began recording all her daily conversations into a journal, in the process preserving an intimate record of her time with Howard. This was useful years later when she wrote of their relationship in a book called One Who Walked Alone, which was the basis for the 1996 film The Whole Wide World starring Vincent D'Onofrio as Howard and Renée Zellweger as Price.

In a review of Michel Houellebecq's essay "H. P. Lovecraft: Against the World, Against Life" published in the Los Angeles Times, April 17, 2005, Stephen King implies that Howard did not work at his craft and was merely pastiching Lovecraft. King described his disapproval of the sword and sorcery genre, and superheroes, in his book on writing Danse Macabre: "[It] is not fantasy at its lowest, but it still has a pretty tacky feel. ... Sword and sorcery novels and stories are tales of power for the powerless. The fellow who is afraid of being rousted by those young punks who hang around his bus stop can go home at night and imagine himself wielding a sword, his potbelly miraculously gone, his slack muscles magically transmuted into those "iron thews" which have been sung and storied in the pulps for the last fifty years." On Howard in particular, he wrote:

Lovecraft scholar S. T. Joshi wrote, in his biography H. P. Lovecraft: A Life, that "The bulk of Howard's fiction is subliterary hackwork that does not even begin to approach genuine literature" and "The simple fact is, however, that his views are not of any great substance or profundity and that Howard's style is crude, slip-shod, and unwieldy. It is all just pulp—although, perhaps, a somewhat superior grade of pulp than the average."

Howard’s suicide and the circumstances surrounding it have led to speculation about his mental health. His mother had been ill with tuberculosis his entire life, and upon learning she had entered a coma from which she was not expected to wake, he walked out to his car and shot himself in the head.