Forster was born into an Anglo-Irish and Welsh family at 6 Melcombe Place, Dorset Square, London NW1, in a building that no longer exists. He was the only child of Alice Clara "Lily" (née Whichelo) and Edward Morgan Llewellyn Forster, an Architect. His name was officially registered as Henry Morgan Forster, but at his baptism he was accidentally named Edward Morgan Forster. To distinguish him from his father, he was always called Morgan. His father died of tuberculosis on 30 October 1880, before Morgan's second birthday. In 1883, Forster and his mother moved to Rooksnest, near Stevenage, Hertfordshire. This house served as a model for Howards End, because he had fond memories of his childhood there. Among Forster's ancestors were members of the Clapham Sect, a social reform group within the Church of England.

He inherited £8,000 (£802,290 as of 2015 of which £1,735,000 were in sovereigns [1883 tr.oz.]) from his paternal great-aunt Marianne Thornton (daughter of the abolitionist Henry Thornton), who died on 5 November 1887. The money was enough to live on and enabled him to become a Writer. He attended Tonbridge School in Kent, as a day boy. The theatre at the school has been named in his honour.

At King's College, Cambridge, between 1897 and 1901, he became a member of a discussion society known as the Apostles (formally named the Cambridge Conversazione Society). They met in secret, and discussed their work on, and about, philosophical and moral questions. Many of its members went on to constitute what came to be known as the Bloomsbury Group, of which Forster was a peripheral member in the 1910s and 1920s. There is a famous recreation of Forster's Cambridge at the beginning of The Longest Journey. The Schlegel sisters of Howards End are based to some degree on Vanessa and Virginia Stephen.

Forster was homosexual (open to his close friends, but not to the public) and a lifelong bachelor. He developed a long-term relationship with Bob Buckingham (1904–1975), a married policeman. Forster included Buckingham and his wife May in his circle, which included J. R. Ackerley, a Writer and literary Editor of The Listener, the Psychologist W. J. H. Sprott and, for a time, the Composer Benjamin Britten. Other Writers with whom Forster associated included Christopher Isherwood, the poet Siegfried Sassoon, and the Belfast-based Novelist Forrest Reid.

His first novel, Where Angels Fear to Tread (1905), is the story of Lilia, a young English widow who falls in love with an Italian, and of the efforts of her bourgeois relatives to get her back from Monteriano (based on San Gimignano). Philip Herriton's mission to retrieve her from Italy has features in Common with that of Lambert Strether in Henry James's The Ambassadors. Forster discussed that work ironically and somewhat disapprovingly in his book Aspects of the Novel (1927). Where Angels Fear to Tread was adapted as a 1991 film directed by Charles Sturridge.

Forster was homosexual, which prompted themes in his works, especially the novel Maurice. Though conscious of his repressed desires, he was thirty-seven before he yielded to them physically. In 1906 he fell in love with Syed Ross Masood, a seventeen-year-old Future Oxford student he tutored in Latin. The Indian had more of a romantic, poetic view of friendship, confusing Forster with constant avowals of his love.

Next, Forster published The Longest Journey (1907), an inverted Bildungsroman following the lame Rickie Elliott from Cambridge to a career as a struggling Writer and then to a post as a schoolmaster, married to the unappealing Agnes Pembroke. In a series of scenes on the hills of Wiltshire, which introduce Rickie's wild half-brother Stephen Wonham, Forster attempts a kind of sublime related to those of Thomas Hardy and D. H. Lawrence.

Forster's third novel, A Room with a View (1908), is his lightest and most optimistic. It was started as early as 1901, before any of his others; its earliest versions are entitled "Lucy". The book explores the young Lucy Honeychurch's trip to Italy with her cousin, and the choice she must make between the free-thinking George Emerson and the repressed aesthete Cecil Vyse. George's father Mr Emerson quotes thinkers who influenced Forster, including Samuel Butler. The book was adapted as a film of the same name in 1985 by the Merchant Ivory team.

Howards End (1910) is an ambitious "condition-of-England" novel concerned with different groups within the Edwardian middle classes, represented by the Schlegels (bohemian intellectuals), the Wilcoxes (thoughtless plutocrats) and the Basts (struggling lower-middle-class aspirants). Critics have observed that numerous characters in Forster's novels die suddenly. This is true of Where Angels Fear to Tread, Howards End and, most particularly, The Longest Journey. Howards End was adapted as a film in 1991 by the Merchant-Ivory team and as a miniseries in 2017. An opera libretto Howards End, America was created in 2016 by Claudia Stevens.

After leaving university, he travelled in continental Europe with his mother. They moved to Weybridge, Surrey where he wrote all six of his novels. In 1914, he visited Egypt, Germany and India with the classicist Goldsworthy Lowes Dickinson, by which time he had written all but one of his novels. In the First World War, as a conscientious objector, Forster volunteered for the International Red Cross, and served in Alexandria, Egypt.

Forster spent a second spell in India in the early 1920s as the private secretary to Tukojirao III, the Maharajah of Dewas. The Hill of Devi is his non-fictional account of this period. After returning to London from India, he completed his last novel, A Passage to India (1924), for which he won the James Tait Black Memorial Prize for fiction. He also edited Eliza Fay's (1756–1816) letters from India, in an edition first published in 1925.

Forster achieved his greatest success with A Passage to India (1924). The novel takes as its subject the relationship between East and West, seen through the lens of India in the later days of the British Raj. Forster connects personal relationships with the politics of colonialism through the story of the Englishwoman Adela Quested, the Indian Dr. Aziz, and the question of what did or did not happen between them in the Marabar Caves. Forster makes special mention of the author Ahmed Ali and his Twilight in Delhi in his Preface to its Everyman's Library Edition. A Passage to India was adapted as a play in 1960, directed by Frank Hauser, and as a film in 1984, directed by David Lean.

In the 1930s and 1940s Forster became a successful broadcaster on BBC Radio and a public figure associated with the Union of Ethical Societies. In addition to being a broadcaster, he advocated individual liberty, penal reform, and opposed censorship, by writing articles, sitting on committees, and signing letters. His weekly book review during the war was commissioned by George Orwell, who was the talks Producer at the Indian Section of the BBC from 1941 to 1943. He was awarded a Benson Medal in 1937.

From 1925 until his mother's death at age 90 on 11 March 1945, Forster lived with her at West Hackhurst, Abinger Hammer, finally leaving on or around 23 September 1946. His London base was 26 Brunswick Square from 1930 to 1939, after which he rented 9 Arlington Park Mansions in Chiswick until at least 1961.

Subsequent books were similarly received on publication. The Manchester Guardian commented on Howards End, describing it as "a novel of high quality written with what appears to be a feminine brilliance of perception... witty and penetrating." An essay by David Cecil in Poets and Storytellers (1949) characterises Forster as "pulsing with intelligence and sensibility", but primarily concerned with an original moral vision: "He tells a story as well as anyone who ever lived".

Forster was President of the Cambridge Humanists from 1959 until his death and a member of the Advisory Council of the British Humanist Association from 1963 until his death. His views as a humanist are at the heart of his work, which often depicts the pursuit of personal connections in spite of the restrictions of contemporary society. His humanist attitude is expressed in the non-fictional essay What I Believe (reprinted with two other humanist essays – and an introduction and notes by Nicolas Walter – as What I Believe, and other essays by the secular humanist publishers G.W. Foote & Co. in 1999). When Forster's cousin, Philip Whichelo, donated a portrait of Forster to the Gay and Lesbian Humanist Association (GLHA), Jim Herrick, the founder, quoted Forster's words: "The humanist has four leading characteristics – curiosity, a free mind, belief in good taste, and belief in the human race."

Forster was elected an honorary fellow of King's College, Cambridge, in January 1946, and lived for the most part in the college, doing relatively little. In April 1947 he arrived in America to begin a three-month nationwide tour of public readings and sightseeing, returning to the East Coast in June. He declined a knighthood in 1949 and was made a Companion of Honour in 1953. At age 82, he wrote his last short story, Little Imber, a science fiction tale. At 85 he went on a pilgrimage to the Wiltshire countryside that had inspired his favourite novel The Longest Journey, escorted by william Golding. In 1969 he was made a member of the Order of Merit. Forster died of a stroke on 7 June 1970 at the age of 91, at the Buckinghams' home in Coventry. His ashes, mingled with those of Buckingham, were later scattered in the rose garden of Coventry's crematorium, near Warwick University.

Maurice (1971) was published posthumously. It is a homosexual love story which also returns to matters familiar from Forster's first three novels, such as the suburbs of London in the English home counties, the experience of attending Cambridge, and the wild landscape of Wiltshire. The novel was controversial, given that Forster's homosexuality had not been previously known or widely acknowledged. Today's critics continue to argue over the extent to which Forster's sexuality and personal activities influenced his writing. Maurice was adapted as a film in 1987 by the Merchant-Ivory team.