Playwright and author S. N. (Samuel Nathaniel) Behrman was born in Worcester, Massachusetts in 1893. He was the youngest of three sons raised by Lithuanian immigrants in the heart of Worcester's Jewish community on Providence Street. An older sister was killed in a streetcar accident during her childhood. The family lived in a tenement which Behrman later mused was "heavily populated with angels," their imaginary presence invoked by the Hebrew prayers of his father, a devout, scholarly man who spent long hours studying the Talmud. As a boy, the precocious Behrman was befriended and mentored by Daniel Asher, a young man six or seven years his senior whom he met through one of his brothers. Under Asher's tutelage, Behrman became a prize-winning leader of his high school debate team. Asher introduced his protégé to the theatre, critiqued his earliest attempts at writing and encouraged him to pursue a literary career.

From 1912-1914, Behrman attended Clark College, where his first essays, short stories and dramatic sketches were published in the student literary magazine. In a 1914 piece entitled "Psychology and the New Philosophy of the Theatre," Behrman praised the work of George Bernard Shaw and Henrik Ibsen, and called for a "progressive ... theatre of ideas." At Daniel Asher's suggestion, Behrman transferred to Harvard College to study drama with George Pierce Baker. He was awarded a B.A. degree in 1916, then moved to New York City where his brothers worked as accountants. They supported him financially while he attended Columbia University and studied French drama under the distinguished Brander Matthews. As Behrman neared the completion of his M.A. degree in the spring of 1918, he was offered a position as English instructor at the University of Minnesota, but turned the job down. He chose to remain in New York to establish himself as a writer.

During the late 1910s, Behrman's short stories and criticism appeared in such magazines as The Seven Arts, The Liberator, The New Republic and The Smart Set. He penned dozens of book reviews for The New York Times, where he worked briefly in the classified advertising department and later as an assistant editor of the book section. Early in 1920, Behrman was sent by the Times to interview the British poet Siegfried Sassoon, then visiting New York on a reading tour. Behrman was deeply moved by Sassoon's passion for literature and by the strong moral sensibility evidenced in his war poems. The two writers spent a great deal of time together while Sassoon was in New York, and they corresponded for many years afterwards. When Behrman later visited England, it was Sassoon who introduced him into intellectual circles that profoundly influenced his writing, advanced his career and enriched his personal life. Behrman's European acquaintances and friends included authors W. Somerset Maugham and Osbert Sitwell; Lydia Keynes, the former ballerina and wife of John Maynard Keynes; and society doyenne Sibyl Colefax.

Through most of the 1920s, Behrman worked in relative obscurity in the midst of the vibrant New York theatre scene. He collaborated on short stories and plays with his friend and occasional roommate Kenyon Nicholson. Their material was frequently published and staged (sometimes under the pen-name Paul Halvy), though to little acclaim. Through Nicholson, Behrman formed a lasting professional association with Harold Freedman, head of the theatre department of the Brandt & Brandt literary agency. He also worked for a time as the press agent of Broadway producer Jed Harris. Behrman stayed in touch with his old friend Daniel Asher, who continued to provide insightful criticism of his work and to profess unequivocal faith in his talent. In August of 1926, as Behrman and playwright Owen Davis put finishing touches to their collaborative work The Man Who Forgot, Asher insisted, with remarkable prescience, that the day was close at hand "when you will work with surging vigor and audacity and the great artistry in you will no longer be denied."

The following spring, Behrman's comedy The Second Man was staged by the Theatre Guild, an important venue for new American drama. The company's acclaimed leading lights, Alfred Lunt and Lynn Fontanne, starred in this successful production which firmly established the playwright's reputation. Based on a short story Behrman had written years before, The Second Man concerns a hack writer faced with a romantic choice between a wealthy woman who supports him financially and a beautiful younger woman who adores him. This portrait of a character in a state of indecision was praised by critics for its cultured, witty dialog and its subtle insight into human psychology. After a six-month New York run, the play toured the United States and was later staged in London with Noël Coward in the lead role.

Behrman followed The Second Man with a string of sophisticated comedies that illuminated the morals, manners and foibles of urbane intellectuals. These included Serena Blandish (1928) with Ruth Gordon in the title role; Brief Moment (1931) with a cameo appearance by drama critic Alexander Woollcott; Biography (1933) starring Ina Claire; End of Summer (1936), also with Claire; and No Time for Comedy (1939) featuring Katherine Cornell and Laurence Olivier. In these popular works, Behrman aimed for a nuanced depiction of the psychological development of his main characters as they strove to achieve worldly success or to find love. In such later plays as I Know My Love (1949) and But For Whom Charlie (1964), Behrman developed an additional theme of the conflict between generations. He rarely set his plays outside of the drawing-rooms of intellectuals and the wealthy, but when he did enlarge his purview he achieved notable success. Fanny (1954), an adaptation (which Behrman co-authored with Joshua Logan) of several of Marcel Pagnol's bawdy seaport stories had a run of more than 800 performances. The Cold Wind and the Warm (1958) drew on experiences from Behrman's youth in Worcester.

During the 1930s and '40s, Behrman spent considerable time in Hollywood, where he wrote or collaborated on numerous screenplays, including Tess of the Storm Country (1932), Anna Karenina (1935) and Waterloo Bridge (1940). He was respected in the movie industry for his sensitive adaptations of literary classics and for his sparkling dialog. Among his friends and colleagues during his Hollywood years were Harpo Marx, Greta Garbo, Salka Viertel and screenwriter Sonya Levien. Back in New York, Behrman was closely associated with dramatists Maxwell Anderson, Sidney Howard, Elmer Rice and Robert E. Sherwood. In 1938 this group established The Playwrights' Company to stage their own work as well as the plays of other authors. Behrman served for awhile as President of the organization, but later resigned his membership over creative differences.

On June 20, 1936, Behrman was married to Elza Heifetz Stone, the recently divorced sister of the famed violinist Jascha Heifetz. A son, Arthur David, was born to the couple the following year, and Behrman became stepfather to two children from his wife's previous marriage. By this time his social set included many prominent actors and actresses, editors, publishers and Hollywood producers. Though he once remarked that he hated to write letters, he nonetheless conducted a broad correspondence with such renowned figures as art critic Bernard Berenson; writer F. Tennyson Jesse; U. S. Supreme Court Justice Felix Frankfurter; lyricist Ira Gershwin; and philosopher Isaiah Berlin. During the 1930s and '40s Behrman wrote numerous letters on behalf of European Jews fleeing Nazi terror and sought to win them entry into the United States.

Throughout his long and prolific career, Behrman continued to write short stories, essays, and criticism. Many of his penetrating biographical sketches, which first appeared in The New Yorker, were eventually collected and published as books. These volumes include Duveen (1952), a portrait of the art dealer Joseph Duveen, Baron of Millbank; The Worcester Account (1954), a collection of poignant autobiographical essays centered on the Providence Street of Behrman's youth; Portrait of Max (1960), about the writer and caricaturist Max Beerbohm; and The Suspended Drawing Room (1965) on subjects ranging from the physician Emanuel Libman to the Hungarian dramatist Ferenc Molnar. Behrman's final dramatic work, But for Whom Charlie, was staged in New York in 1964, but received poor reviews. He subsequently focused most of his energy on narrative prose, producing a loosely autobiographical novel, The Burning Glass (1968), as well as introductions to anthologies of Horatio Alger stories and old articles from The Smart Set. Behrman spent his last years mining the meticulous diaries he had kept since college, resulting in the memoir People in a Diary (1972).