Born at 31 Augustus Road, Edgbaston, Birmingham,as Mary Barbara Hamilton. she was the only daughter and eldest child of a British army officer, Major Bertram Cartland (born James Bertram Falkner Cartland, 1876 died 27 May 1918), and his wife, Mary Polly Hamilton Scobell (1877–1976). Though she was born into an enviable degree of middle-class comfort, the family's security was severely shaken after the suicide of her paternal grandfather, James Cartland, a financier, who shot himself in the wake of bankruptcy.

This was followed soon after by her father's death on a Flanders battlefield in World War I. However, her enterprising mother opened a London dress shop to make ends meet — "Poor I may be," Polly Cartland once remarked, "but common I am not" — and to raise Cartland and her two brothers, Anthony and Ronald, both of whom were eventually killed in battle, one day apart, in 1940.

After attending The Alice Ottley School, Malvern Girls' College and Abbey House, an educational institution in Hampshire, Cartland soon became successful as a society reporter and writer of romantic fiction. Cartland admitted she was inspired in her early work by the novels of Edwardian author Elinor Glyn, whom she idolized and eventually befriended.

After a year as a gossip columnist for the Daily Express, Cartland published her first novel, Jigsaw (1923), a risqué society thriller that became a bestseller. She also began writing and producing somewhat racy plays, one of which, Blood Money (1926), was banned by the Lord Chamberlain's Office. In the 1920s and '30s Cartland was one of the leading young hostesses in London society, noted for her beauty, energetic charm and daring parties. Her fashion sense also had a part in launching her fame and she was one of the first clients of designer Sir Norman Hartnell, remaining a client until he died in 1979. He made her presentation and wedding dresses, the latter was made to her own design against Hartnell's wishes and she admitted it was a failure.

Barbara Cartland's image as a self-appointed "expert" on romance drew some ridicule in her later years, when her social views became more conservative. Indeed, although her first novels were considered sensational, Barbara Cartland's later (and arguably most popular) titles were comparatively tame with virginal heroines and few, if any, suggestive situations. Almost all of Cartland's later books were historical in theme, which allowed for the believability of chastity (at least, to many of her audience).

Despite their tame story lines, Barbara Cartland's later novels were highly successful. By 1983 she rated the longest entry in the British Who's Who (though most of that article was a list of her books), and was named the top-selling author in the world by the Guinness Book of World Records. In the mid-1990s, by which time she had sold over a billion books, Vogue magazine called her "the true Queen of Romance". She became a mainstay of the popular media in her trademark pink dresses and plumed hats, discoursing on matters of love, marriage, politics, religion, health and fashion. She was publicly opposed to the removal of prayer from state schools and spoke against infidelity and divorce, although she admitted to being acquainted with both of these moral failings.

Privately, Cartland took an interest in the early gliding movement. Although aerotowing for launching gliders first occurred in Germany, she thought of long distance tows in 1931 and did a 200-mile (360 km) tow in a two-seater glider. The idea led to troop-carrying gliders. In 1984, she was awarded the Bishop Wright Air Industry Award for this contribution.

She regularly attended Brooklands aerodrome and motor racing circuit during the 1920s and 1930s, and the Brooklands Museum has preserved a sitting room from that era and named it after her.

According to an obituary published in The Daily Telegraph on 22 May 2000, Cartland reportedly broke off her first engagement, to a Guards officer, when she learned about sexual intercourse and recoiled. This claim fits in with her image as part of a generation for whom such matters were never discussed, but sits uneasily with her having produced work controversial at the time for its sexual subject matter, as described above. In any case, she was married, from 1927 to 1932, to Alexander George McCorquodale (died 1964), a British Army officer and heir to a British printing fortune.

Their daughter, Raine McCorquodale (born in 1929), became "Deb of the Year" in 1947. After the McCorquodales' 1936 divorce, which involved charges and countercharges of infidelity, Cartland married a man her husband had accused her of dallying with — his cousin Hugh McCorquodale, a former military officer. She and her second husband, who died in 1963, had two sons, Ian and Glen McCorquodale.