The location of her birth remains uncertain, but reputedly she was born either in her parents' Westminster home at Belgrave Mansions, Grosvenor Gardens, or in a horse-drawn ambulance on the way to a hospital. Other possible locations include Forbes House in Ham, London, the home of her maternal grandmother, Louisa Scott. Her birth was registered at Hitchin, Hertfordshire, near the Strathmores' English country house, St Paul's Walden Bury, which was also given as her birthplace in the census the following year. She was christened there on 23 September 1900, in the local parish church, All Saints, and her godparents included her paternal aunt Lady Maud Bowes-Lyon and cousin Venetia James.

On her fourteenth birthday, Britain declared war on Germany. Four of her brothers served in the army. Her elder brother, Fergus, an officer in the Black Watch Regiment, was killed in action at the Battle of Loos in 1915. Another brother, Michael, was reported missing in action on 28 April 1917. Three weeks later, the family discovered he had been captured after being wounded. He remained in a prisoner of war camp for the rest of the war. Glamis was turned into a convalescent home for wounded Soldiers, which Elizabeth helped to run. She was particularly instrumental in organising the rescue of the castle's contents during a serious fire on 16 September 1916. One of the Soldiers she treated wrote in her autograph book that she was to be "Hung, drawn, & quartered ... Hung in diamonds, drawn in a coach and four, and quartered in the best house in the land."

In February 1922, Elizabeth was a bridesmaid at the wedding of Albert's sister, Princess Mary, to Viscount Lascelles. The following month, Albert proposed again, but she refused him once more. Eventually, in January 1923, Elizabeth agreed to marry Albert, despite her misgivings about royal life. Albert's freedom in choosing Elizabeth, not a member of a royal family, though the daughter of a peer, was considered a gesture in favour of political modernisation; previously, princes were expected to marry princesses from other royal families. They selected a platinum engagement ring featuring a Kashmir Sapphire with two diamonds adorning its sides.

They married on 26 April 1923, at Westminster Abbey. Unexpectedly, Elizabeth laid her bouquet at the Tomb of the Unknown Warrior on her way into the Abbey, in memory of her brother Fergus. Elizabeth became styled Her Royal Highness The Duchess of York. Following a wedding breakfast at Buckingham Palace prepared by chef Gabriel Tschumi, the new Duchess and her husband honeymooned at Polesden Lacey, a manor house in Surrey, and then went to Scotland, where she caught "unromantic" whooping cough.

After a successful visit to Northern Ireland in July 1924, the Labour government agreed that Albert and Elizabeth could tour East Africa from December 1924 to April 1925. The Labour government was defeated by the Conservatives in a general election in November (which Elizabeth described as "marvellous" to her mother) and the Governor-General of Anglo-Egyptian Sudan, Sir Lee Stack, was assassinated three weeks later. Despite this, the tour went ahead, and they visited Aden, Kenya, Uganda, and Sudan, but Egypt was avoided because of political tensions.

Albert had a stammer, which affected his ability to deliver speeches, and after October 1925, Elizabeth assisted in helping him through the therapy devised by Lionel Logue, an episode portrayed in the 2010 film The King's Speech. In 1926, the couple had their first child, Princess Elizabeth—"Lilibet" to the family—who would later become Queen Elizabeth II. Another daughter, Princess Margaret Rose, was born four years later. Albert and Elizabeth, without their child, travelled to Australia to open Parliament House in Canberra in 1927. She was, in her own words, "very miserable at leaving the baby". Their journey by sea took them via Jamaica, the Panama Canal and the Pacific; Elizabeth fretted constantly over her baby back in Britain, but their journey was a public relations success. She charmed the public in Fiji when, shaking hands with a long line of official guests, a stray dog walked in on the ceremony and she shook its paw as well. In New Zealand she fell ill with a cold and missed some engagements, but enjoyed the local fishing in the Bay of Islands accompanied by Australian Sports Fisherman Harry Andreas. On the return journey, via Mauritius, the Suez Canal, Malta and Gibraltar, their transport, HMS Renown, caught fire and they prepared to abandon ship before the fire was brought under control.

Rather than abandon his plans to marry Simpson, he chose to abdicate in favour of Albert, who reluctantly became King in his place on 11 December 1936 under the regnal name of George VI. George VI and Elizabeth were crowned King and Queen of Great Britain, Ireland and the British Dominions, and Emperor and Empress of India in Westminster Abbey on 12 May 1937, the date previously scheduled for Edward VIII. Elizabeth's crown was made of platinum and was set with the Koh-i-Noor Diamond.

The Cunard White Star Line's RMS Queen Elizabeth was named after her. She launched the ship on 27 September 1938 in Clydebank, Scotland. Supposedly, the liner started to slide into the water before Elizabeth could officially launch her, and acting sharply, she managed to smash a bottle of Australian red over the liner's bow just before it slid out of reach. In 1954, Queen Elizabeth sailed to New York on her namesake.

In May and June 1939, Elizabeth and her husband toured Canada from coast to coast and back, and visited the United States, spending time with President Roosevelt at the White House and his Hudson Valley estate. U.S. First Lady Eleanor Roosevelt said that Elizabeth was "perfect as a Queen, gracious, informed, saying the right thing & kind but a little self-consciously regal". The tour was designed to bolster trans-Atlantic support in the event of war, and to affirm Canada's status as an independent kingdom sharing with Britain the same person as monarch.

In the 1945 British general election, Churchill's Conservative party was soundly defeated by the Labour party of Clement Attlee. Elizabeth's political views were rarely disclosed, but a letter she wrote in 1947 described Attlee's "high hopes of a socialist heaven on earth" as fading and presumably describes those who voted for him as "poor people, so many half-educated and bemused. I do love them." Woodrow Wyatt thought her "much more pro-Conservative" than other members of the royal family, but she later told him, "I like the dear old Labour Party." She also told the Duchess of Grafton, "I love communists".

She oversaw the restoration of the remote Castle of Mey, on the north coast of Scotland, which she used to "get away from everything" for three weeks in August and ten days in October each year. She developed her interest in horse racing, particularly steeplechasing, which had been inspired by the amateur jockey Lord Mildmay in 1949.

During the 1947 royal tour of South Africa, Elizabeth's serene public behaviour was broken, exceptionally, when she rose from the royal car to strike an admirer with her umbrella because she had mistaken his enthusiasm for hostility. The 1948 royal tour of Australia and New Zealand was postponed because of the King's declining health. In March 1949, he had a successful operation to improve the circulation in his right leg. In summer 1951, Queen Elizabeth and her daughters fulfilled the King's public engagements in his place. In September, he was diagnosed with lung cancer. After a lung resection, he appeared to recover, but the delayed trip to Australia and New Zealand was altered so that Princess Elizabeth and her husband, the Duke of Edinburgh, went in the King and Queen's place, in January 1952. The King died in his sleep on 6 February 1952 while Princess Elizabeth and the Duke of Edinburgh were in Kenya en route to the southern hemisphere, and they returned immediately to London, as queen and Prince consort.

She was devastated by her husband's death and retired to Scotland. However, after a meeting with the Prime Minister, Winston Churchill, she broke her retirement and resumed her public duties. Eventually she became just as busy as queen mother as she had been as queen consort. In July 1953, she undertook her first overseas visit since the funeral when she visited the Federation of Rhodesia and Nyasaland with Princess Margaret. She laid the foundation stone of the University College of Rhodesia and Nyasaland – the current University of Zimbabwe.

Upon her return to the region in 1957, she was inaugurated as the College's President, and attended other events that were deliberately designed to be multi-racial. During her daughter's extensive tour of the Commonwealth over 1953–54, Elizabeth acted as a Counsellor of State and looked after her grandchildren, Charles and Anne.

In February 1964, she had an emergency appendectomy, which led to the postponement of a planned tour of Australia, New Zealand and Fiji until 1966. She recuperated during a Caribbean cruise aboard the royal yacht, Britannia. In December 1966, she underwent an operation to remove a tumour after she was diagnosed with colon cancer. Contrary to rumours, she did not have a colostomy. In 1984, she was diagnosed with breast cancer and a lump was removed from her breast. Her bouts with cancer were never made public during her lifetime.

Sir Hugh Casson said Elizabeth was like "a wave breaking on a rock, because although she is sweet and pretty and charming, she also has a basic streak of toughness and tenacity. ... when a wave breaks on a rock, it showers and Sparkles with a brilliant play of foam and droplets in the sun, yet beneath is really hard, tough rock, fused, in her case, from strong principles, physical courage and a sense of duty." Sir Peter Ustinov described her during a student demonstration at the University of Dundee in 1968:

After being advised by a Conservative Minister in the 1970s not to employ homosexuals, the Queen Mother observed that without them, "we'd have to go self-service". On the fate of a gift of a nebuchadnezzar of champagne (20 bottles' worth) even if her family did not come for the holidays, she said, "I'll Polish it off myself." Emine Saner of The Guardian suggests that with a gin and Dubonnet at noon, red wine with lunch, a port and martini at 6 pm and two glasses of champagne at dinner, "a conservative estimate puts the number of alcohol units she drank at 70 a week". Her lifestyle amused journalists, particularly when it was revealed she had a multi-million pound overdraft with Coutts Bank.

In 1975, she visited Iran at the invitation of Shah Mohammad Reza Pahlavi. The British ambassador and his wife, Anthony and Sheila Parsons, noted how the Iranians were bemused by her habit of speaking to everyone regardless of status or importance, and hoped the Shah's entourage would learn from the visit to pay more attention to ordinary people. Between 1976 and 1984, she made annual summer visits to France, which were among 22 private trips to continental Europe between 1963 and 1992.

Her habits were parodied by the satirical 1980s television programme Spitting Image. She was portrayed by Juliet Aubrey in Bertie and Elizabeth, Sylvia Syms in The Queen, Natalie Dormer in W.E., Olivia Colman in Hyde Park on Hudson, Victoria Hamilton in The Crown, and in The King's Speech by Helena Bonham Carter, who was nominated for an Academy Award for Best Supporting Actress and won a BAFTA Award for Best Actress in a Supporting Role for her portrayal.

In 1982, she was rushed to hospital when a fish bone became stuck in her throat, and had an operation to remove it. Being a keen angler, she calmly joked afterwards, "The salmon have got their own back." Similar incidents occurred at Balmoral in August 1986, when she was hospitalised at Aberdeen Royal Infirmary overnight but no operation was needed, and May 1993, when she was admitted to the Infirmary for surgery under general anaesthetic.

She owned the winners of approximately 500 races. Her distinctive colours of blue with buff stripes were carried by horses such as Special Cargo, the winner of the 1984 Whitbread Gold Cup, and Devon Loch, which spectacularly halted just short of the winning post at the 1956 Grand National and whose jockey Dick Francis later had a successful career as the Writer of racing-themed detective stories. Peter Cazalet was her trainer for over 20 years. Although (contrary to rumour) she never placed bets, she did have the racing commentaries piped direct to her London residence, Clarence House, so she could follow the races. As an art collector, she purchased works by Claude Monet, Augustus John and Peter Carl Fabergé, among others.

In 1987, she was criticised when it emerged that two of her nieces, Katherine and Nerissa Bowes-Lyon, had both been committed to a psychiatric hospital because they were severely handicapped. However, Burke's Peerage had listed the sisters as dead, apparently because their mother, Fenella (the Queen Mother's sister-in-law), "was 'extremely vague' when it came to filling in forms and might not have completed the paperwork for the family entry correctly". When Nerissa died the year before, her grave was originally marked with a plastic tag and a serial number. The Queen Mother said that the news of their institutionalisation came as a surprise to her.

In her later years, the Queen Mother became known for her longevity. Her 90th birthday—4 August 1990—was celebrated by a parade on 27 June that involved many of the 300 organisations of which she was patron. In 1995, she attended events commemorating the end of the war fifty years before, and had two operations: one to remove a cataract in her left eye, and one to replace her right hip. In 1998, her left hip was replaced after it was broken when she slipped and fell during a visit to Sandringham stables.

Her 100th birthday was celebrated in a number of ways: a parade that celebrated the highlights of her life included contributions from Sir Norman Wisdom and Sir John Mills; her image appeared on a special commemorative £20 note issued by the Royal Bank of Scotland; and she attended a lunch at the Guildhall, London, at which George Carey, the Archbishop of Canterbury, accidentally attempted to drink her glass of wine. Her quick admonition of "That's mine!" caused widespread amusement. In November 2000, she broke her collarbone in a fall that kept her recuperating at home over Christmas and the New Year.

On 1 August 2001, she had a blood transfusion for anaemia after suffering from mild heat exhaustion, though she was well enough to make her traditional appearance outside Clarence House three days later to celebrate her 101st birthday. Her final public engagements included planting a cross at the Field of Remembrance on 8 November 2001; a reception at the Guildhall, London, for the reformation of the 600 Squadron, Royal Auxiliary Air Force on 15 November; and attending the re-commissioning of HMS Ark Royal on 22 November.

On 30 March 2002, at 15:15 (GMT), the Queen Mother died in her sleep at the Royal Lodge, Windsor Great Park, with her surviving daughter, Queen Elizabeth II, at her bedside. She had been suffering from a cold for the previous four months. At 101 years and 238 days old she was the longest-lived member of the royal family in British history. Her last surviving sister-in-law Princess Alice, Duchess of Gloucester, exceeded that, dying aged 102 on 29 October 2004.

A statue of Queen Elizabeth The Queen Mother by Sculptor Philip Jackson was unveiled in front of the George VI Memorial, off The Mall, London, on 24 February 2009, creating the George VI and Queen Elizabeth Memorial.

In March 2011, her eclectic musical taste was revealed when details of her small record collection kept at the Castle of Mey were made public. Her records included ska, local folk, Scottish reels and the musicals Oklahoma! and The King and I, and artists such as yodeller Montana Slim, Tony Hancock, The Goons and Noël Coward.

Elizabeth—known for her personal and public charm—was one of the most popular members of the royal family, and helped to stabilise the popularity of the monarchy as a whole.