Beaton was born on 14 January 1904 in Hampstead the son of Ernest Walter Hardy Beaton (1867–1936), a prosperous timber merchant, and his wife Etty Sissons (1872–1962). His grandfather, Walter Hardy Beaton (1841–1904) had founded the family business of Beaton Brothers Timber Merchants and Agents, and his father followed into the business. Ernest Beaton was also an amateur actor and had met his wife, Cecil's mother, when playing the lead in a play. She was the daughter of a Cumbrian blacksmith who had come to London to visit her married sister. They had four children - in addition to Cecil there were two daughters Nancy (1909–1999) and Baba (1912–1973), and another son Reggie (1905–1933). Cecil Beaton was educated at Heath Mount School (where he was bullied by Evelyn Waugh) and St Cyprian's School, Eastbourne, where his artistic talent was quickly recognised. Both Cyril Connolly and Henry Longhurst report in their autobiographies being overwhelmed by the beauty of Beaton's singing at the St Cyprian's school concerts. When Beaton was growing up his Nanny had a Kodak 3A Camera, a popular model which was renowned for being an ideal piece of equipment to learn on. Beaton's nanny began teaching him the basics of photography and developing film. He would often get his sisters and mother to sit for him. When he was sufficiently proficient, he would send the photos off to London society magazines, often writing under a pen name and ‘recommending’ the work of Beaton.

Beaton went on to Harrow, and then, despite having little or no interest in academia, moved on to St John's College, Cambridge, and studied history, art and architecture. Beaton continued his photography, and through his university contacts managed to get a portrait sitting with the Duchess of Malfi — actually George "Dadie" Rylands, and as Beaton recalled years later: "It was a slightly out-of-focus snapshot of him as Webster's Duchess of Malfi standing in the sub-aqueous light outside the men's lavatory of the ADC Theatre at Cambridge." The resulting images gave Beaton his first ever piece of published work when Vogue magazine bought and printed the photos.

Beaton left Cambridge without a degree in 1925, but only coped with salaried employment in his father's timber business for eight days. His brother Reggie however entered the business and remained until his death in October 1933.

For fifteen years between 1930 and 1945, Beaton leased Ashcombe House in Wiltshire, where he entertained many notable figures.

Beaton designed book jackets and costumes for charity matinees, learning the professional craft of photography at the studio of Paul Tanqueray, until Vogue took him on regularly in 1927. He also set up his own studio, and one of his earliest clients and, later, best friends was Stephen Tennant; Beaton's photographs of Tennant and his circle are considered some of the best representations of the Bright Young People of the twenties and thirties.

He was a photographer for the British edition of Vogue in 1931 when George Hoyningen-Huene, photographer for the French Vogue traveled to England with his new friend Horst. Horst himself would begin to work for French Vogue in November of that year. The exchange and cross pollination of ideas between this collegial circle of artists across the Channel and the Atlantic gave rise to the look of style and sophistication for which the 1930s are known.

Beaton is best known for his fashion photographs and society portraits. He worked as a staff photographer for Vanity Fair and Vogue in addition to photographing celebrities in Hollywood.

Beaton's first camera was a Kodak 3A folding camera. Over the course of his career, he employed both large format cameras, and smaller Rolleiflex cameras. Beaton was never known as a highly skilled technical photographer, and instead focused on staging a compelling model or scene and looking for the perfect shutter-release moment.

Beaton often photographed the Royal Family for official publication. Queen Elizabeth, the Queen Mother was his favourite Royal sitter, and he once pocketed her scented hankie as a keepsake from a highly successful shoot. Beaton took the famous wedding pictures of the Duke and Duchess of Windsor (wearing an ensemble by the noted fashion designer Mainbocher).

During the Second World War, Beaton was initially posted to the Ministry of Information and given the task of recording images from the home front. During this assignment he captured one of the most enduring images of British suffering during the war, that of three-year-old Blitz victim Eileen Dunne recovering in hospital, clutching her beloved teddy bear. When the image was published, America had not yet officially joined the war—but splashed across the press in the US, images such as Beaton’s helped push the American public to put pressure on their Government to help Britain in its hour of need.