Brooks was born as Reuben Sax to Hyman and Esther Sax, Russian Jewish immigrants. Married teenagers when they immigrated to the United States in 1908, they found employment in Philadelphia's textile and clothing industry. Their only child Reuben Sax was born in 1912 in Philadelphia. He attended public schools Joseph Leidy Elementary, Mayer Sulzberger Junior High School and West Philadelphia High School, graduating from the latter in 1929.

Brooks was developing a reputation as a hard-driving, difficult and perpetually angry man as early as his tenure with radio station WNEW in the late 1930s. He was not averse to quitting a job when in conflict with those in charge—as he did while directing at the Mill Pond Theater in 1940 and writing for Universal in 1943. At MGM he was known for almost daily eruptions of anger, often aimed at his crew and sometimes at his cast. That did not change even after he was the Producer of his films, and he was known throughout the industry as a talented filmmaker yet a difficult man to deal with. Many people also found him trustworthy, generous and loyal and thought his temperament was a way of blowing off steam as well as fending off those who wanted to diminish his creative power or try to control him.

Brooks also began writing plays in 1938 and tried directing for Long Island's Mill Pond Theater in 1940. A falling out with his theater colleagues that summer led him to drive to Los Angeles on a whim, hoping to find work in the film industry. He also may have been trying to escape a marriage; a legal document indicates he was married at least part of the time he lived in New York.

While he worked in the studio system for most of the 1940s and 1950s, Brooks often clashed with studio policies about the look and feel of films and the stories they presented. He also chafed against the Production Code's limitations on subject matter and expression. His goal as a filmmaker was total control of a production, and he achieved that with most films after the success of Cat on a Hot Tin Roof. The failure of Lord Jim threatened that independence. Brooks responded by becoming a fast and efficient filmmaker, operating with a tight budget and often forgoing a high up-front salary in exchange for a guarantee of control.

He didn't find film work but was hired by the NBC affiliate to write original stories and read them for a daily fifteen-minute broadcast called Sidestreet Vignettes. His second marriage, in 1941, to Jeanne Kelly, an Actress at Universal Studios, may have helped to open the door to writing for the studio. He contributed dialogue to a few films and wrote two screenplays for the popular Actress Maria Montez, known as the "Queen of Technicolor." With no prospect of moving into more prestigious productions, he quit Universal and joined the Marine Corps in 1943 during World War II.

Brooks never served overseas during the war, instead working in the Marine Corps film unit at Quantico, Virginia, and at times at Camp Pendleton, California. In his two years in uniform he learned more about the basics of filmmaking, including writing and editing documentaries. He also found time to write a novel, The Brick Foxhole, a searing portrait of stateside Soldiers tainted by religious, racial and homophobic bigotry. In 1944 he divorced his wife, then known in films as Jean Brooks. Later he said he had been a self-centered husband and unsuitable for what she needed.

His book was published in 1945 to favorable reviews. It was adapted as the film Crossfire (1947), the first major Hollywood film to deal with anti-Semitism, receiving an Oscar nomination. The novel drew the attention of independent Producer Mark Hellinger, who hired Brooks as a Screenwriter after he left the Marines.

Working for Hellinger brought Brooks back to the film industry and led to a long friendship with actor Humphrey Bogart, a close friend of the Producer. Brooks provided an uncredited screen story for The Killers (1946), which introduced actor Burt Lancaster. He wrote the scripts for two other Hellinger films, notably Brute Force (1947), also starring Lancaster. After Hellinger died suddenly in 1947, Brooks wrote screenplays for three Warner Brothers films, including Key Largo (1948), starring Bogart and wife Lauren Bacall and directed and co-written by John Huston, another Brooks mentor. He was the only co-writer Brooks ever had. Huston allowed Brooks to be on the Key Largo set during shooting so that he could learn more about directing a Hollywood film.

Brooks wrote two more novels shortly after the war, The Boiling Point (1948) and The Producer (1951), a thinly disguised portrait of Hellinger. It may also have contained autobiographical elements about Brooks. In 1946 he married again, to Harriette Levin, who had no apparent connection to the film industry. Their marriage lasted until 1957, when she sought a default divorce.

Success as a Screenwriter with Hellinger and Warner Brothers led Brooks to a contract with MGM and the promise of a chance to direct a film. He wrote two screenplays for the studio before he was given the opportunity to direct. His first film as Writer and Director, Crisis (1950), starred Cary Grant as a brain surgeon forced to save the life of a South American dictator, played by José Ferrer. His second film, The Light Touch (1951), starring Stewart Granger, was a caper film about art thieves and was shot in Italy.

Brooks hated bigotry, which was a central theme of his novel The Brick Foxhole, his co-written screenplay for Storm Warning (1951), and his first western, The Last Hunt (1956). Racial division and reconciliation was also at the heart of Something of Value (1957). He saw Blackboard Jungle as encouraging teachers to continue striving to help their students and as reassuring them that they can make a difference. Opposed to the death penalty, he used In Cold Blood to suggest that executing Criminals solves nothing and only creates more violence.

In 1955, Brooks was one of four American auteur filmmakers named as rebels by the French magazine Cahiers du Cinéma. Box-office success was what gave the writer/director more freedom at MGM, but Brooks also recognized that he would never have complete control of his films while under contract. He avoided writing original screenplays and focused on adaptations of best-sellers or classic novels. He later noted that adapting a novel gave him a head start on developing the story structure required for a screenplay.

He spent the rest of the decade at MGM, when his most notable film was an adaptation of Tennessee Williams's sexually charged play Cat on a Hot Tin Roof (1958). A huge hit for MGM – it drew more money and a larger audience than any other film Brooks ever directed – the film revived the career of Elizabeth Taylor and made a star of Paul Newman. It brought Brooks his first Oscar nomination for directing and the first Best Picture nomination for a film he had directed.

Brooks was one of the relatively few filmmakers whose careers bridged the transition from the classic studio system to the independent productions that marked the 1960s and beyond. He was also among the postwar writer-directors who made some of their best films as they struggled to break free of industry censorship. His legacy is that of a filmmaker who sought independence in a collaborative art and tried to bring his own vision to the screen.

Brooks adapted and directed another Tennessee Williams play, Sweet Bird of Youth (1962). Ed Begley won a Best Supporting Oscar for his role in the film. While popular and well-received critically, the MGM production did not duplicate the success of the previous Williams film. A dream project followed, an adaptation for Columbia Pictures of Joseph Conrad's Lord Jim (1965), but the lavish film proved to be a misfire at the box office and with most critics. Brooks had spent years writing the script and planning the most expensive project of his career. He had assembled a stellar cast led by Peter O'Toole, Eli Wallach, Jack Hawkins, Paul Lukas, and James Mason. While beautifully photographed in Hong Kong and Southeast Asia by Freddie Young and scored by Bronislau Kaper, Lord Jim did not find the audience that had made David Lean's epics Lawrence of Arabia and Doctor Zhivago such notable hits of the 1960s.

To recover professionally from the failure of Lord Jim, Brooks surprised Hollywood by choosing to adapt a minor western novel about a wealthy husband who hires mercenaries to rescue his kidnapped wife from Mexican bandits. Brooks worked quickly and within a year released The Professionals (1966), which became Columbia's biggest hit that year. The slick crowd-pleaser starred Burt Lancaster, Lee Marvin, Robert Ryan and Woody Strode as "the professionals" with Jack Palance as the bandit leader and Claudia Cardinale as the kidnapped wife. The film received Oscar nominations for Brooks' screenplay and direction, and for Conrad Hall's cinematography. It has been lauded as one of the most entertaining westerns ever filmed.

The Professionals and In Cold Blood marked the apex of Brooks' career. In the two decades that followed, he wrote and directed just six more films. Of note was The Happy Ending (1969). From his original screenplay about a woman dealing with disappointments in her marriage and her life, it was the kind of low-key personal film more likely to come from Europe than an American Director. The film earned an Oscar nomination for star Jean Simmons. (Her own marriage to Brooks ended in divorce in 1980.)

Bite the Bullet (1975) was Brooks' return to the western. He based his original screenplay on the endurance horse races popular at the turn of the century. In 1977, he released another controversial film, an adaptation of Judith Rossner's 1975 novel Looking for Mr. Goodbar. It starred Diane Keaton as a Catholic school Teacher who searches for sexual satisfaction in singles bars. Brooks made the film on a tight budget, and its frank treatment of sex and its horrific storyline brought praise and condemnation and sold tickets. He ended his career with Wrong Is Right (1982), a satire about the news media and world unrest starring Sean Connery, and a gambling addiction film, Fever Pitch (1985). Both were critical and commercial failures.

Surrounded by family (Jean Simmons and daughters) and longtime friend actor Gene Kelly, Brooks died from congestive heart failure in 1992 at his house in Coldwater Canyon in Studio City, California. He was interred in the Hillside Memorial Park Cemetery in Culver City, California, a few steps away from the graves of his parents. On his vault was placed a plaque inscribed, "First comes the word. . .". The quote was chosen by his step-daughter, film Editor Tracy Granger, as Brooks always identified most strongly as a Writer.

No matter what the medium – newspapers, radio, novels, film – Brooks considered himself a storyteller. He believed his work should be and was truthful at its core. He also sought to use film as well as other media to say something he believed was important. While his films were easily categorized by genre and were most often based on another writer's story, his screenplays often became vehicles for a message he wanted to offer to audiences.