Eliot was born into the Eliot family of St. Louis, Missouri. His father, Henry Ware Eliot (1843–1919), was a successful businessman, president and treasurer of the Hydraulic-Press Brick Company in St. Louis; his mother, born Charlotte Champe Stearns (1843–1929), wrote poems and was also a social worker. Eliot was the last of six surviving children; his parents were both 44 years old when he was born. His four sisters were between eleven and nineteen years older than he; his brother was eight years older. Known to family and friends as Tom, he was the namesake of his maternal grandfather Thomas Stearns.
From 1898 to 1905 Eliot was a student at Smith Academy, a preparatory school for Washington University. At the academy, Eliot studied Latin, Greek, French, and German. Upon graduation he could have gone to Harvard University but his parents sent him to Milton Academy (in Milton, Massachusetts, near Boston) for a preparatory year. There he met Scofield Thayer, who would later publish The Waste Land. He studied at Harvard from 1906 to 1909, where he earned an A.B.. During this time he read Arthur Symons's The Symbolist Movement in Literature, where he first encountered Laforgue, Rimbaud, and Verlaine. The Harvard Advocate published some of his poems and he became lifelong friends with Conrad Aiken. The following year he earned a master's degree at Harvard. During the 1910–1911 school year Eliot lived in Paris, studying at the Sorbonne and touring the continent.
Returning to Harvard in 1911 as a student in philosophy, Eliot studied the writings of F. H. Bradley, Buddhism and Indic philology (learning Sanskrit and Pāli to read some of the religious texts). He was awarded a scholarship to Merton College, Oxford in 1914. Before settling there he visited Marburg, Germany, where he planned to take a summer program in philosophy. When the First World War broke out, however, he went to London and then to Oxford.
In a letter to Aiken late in December 1914, Eliot, aged 26, wrote "I am very dependent upon women (I mean female society)" and then added a complaint that he was still a virgin. Less than four months later Thayer introduced Eliot to Cambridge governess Vivienne Haigh-Wood. Eliot was not happy at Merton and declined a second year there. On 26 June 1915 he married Vivienne in a register office. After a short unaccompanied visit to see his family in the U.S., he returned to London and took several teaching jobs such as lecturing at Birkbeck College, University of London. He continued to work on his dissertation and, in the spring of 1916, submitted it to Harvard. Because he did not appear in person to defend his dissertation, however, he was not awarded his PhD. (In 1964 the dissertation was published as Knowledge and Experience in the Philosophy of F. H. Bradley.) During his university career Eliot studied with George Santayana, Irving Babbitt, Henri Bergson, C. R. Lanman, Josiah Royce, Bertrand Russell, and Harold Joachim.
Bertrand Russell took an interest in Vivien (the spelling she preferred) while the newlyweds stayed in his flat. Some scholars have suggested that Vivien and Russell had an affair (see Carole Seymour-Jones, Painted Shadow), but these allegations have never been confirmed. In a private paper written in his sixties Eliot confessed: "I came to persuade myself that I was in love with Vivienne simply because I wanted to burn my boats and commit myself to staying in England. And she persuaded herself (also under the influence of Pound) that she would save the poet by keeping him in England. To her, the marriage brought no happiness. To me, it brought the state of mind out of which came The Waste Land."
After leaving Merton, Eliot worked as a schoolteacher, most notably at Highgate School (where he taught the young John Betjeman) and later at the Royal Grammar School, High Wycombe. To earn extra money he wrote book reviews and lectured at evening extension courses. In 1917 he took a position at Lloyds Bank in London, working on foreign accounts. On a trip to Paris during August 1920 Eliot met James Joyce and Wyndham Lewis. After the meeting Eliot said he found Joyce arrogant (Joyce doubted Eliot's ability as a poet at the time), but the two soon became friends, with Eliot visiting Joyce whenever he was in Paris. In 1925 Eliot left Lloyds to join the publishing firm Faber and Gwyer (later Faber and Faber), where he remained for the rest of his career, eventually becoming a director of the firm. Wyndham Lewis and Eliot became close friends, a friendship leading to the well-known painting produced in 1938.