Victoria turned 18 on 24 May 1837, and a regency was avoided. On 20 June 1837, William IV died at the age of 71, and Victoria became Queen of the United Kingdom. In her diary she wrote, "I was awoke at 6 o'clock by Mamma, who told me the Archbishop of Canterbury and Lord Conyngham were here and wished to see me. I got out of bed and went into my sitting-room (only in my dressing gown) and alone, and saw them. Lord Conyngham then acquainted me that my poor Uncle, the King, was no more, and had expired at 12 minutes past 2 this morning, and consequently that I am Queen."[33] Official documents prepared on the first day of her reign described her as Alexandrina Victoria, but the first name was withdrawn at her own wish and not used again.[34] Since 1714, Britain had shared a monarch with Hanover in Germany, but under Salic law women were excluded from the Hanoverian succession. While Victoria inherited all the British dominions, Hanover passed instead to her father's younger brother, her unpopular uncle the Duke of Cumberland and Teviotdale, who became King Ernest Augustus I of Hanover. He was her heir presumptive until she had a child.[35]

At the time of her accession, the government was led by the Whig prime minister Lord Melbourne, who at once became a powerful influence on the politically inexperienced Queen, who relied on him for advice.[36] Charles Greville supposed that the widowed and childless Melbourne was "passionately fond of her as he might be of his daughter if he had one", and Victoria probably saw him as a father figure.[37] Her coronation took place on 28 June 1838, and she became the first sovereign to take up residence at Buckingham Palace.[38] She inherited the revenues of the duchies of Lancaster and Cornwall, and was granted a civil list of £385,000 per year. Financially prudent, she paid off her father's debts.[39] At the start of her reign Victoria was popular,[40] but her reputation suffered in an 1839 court intrigue when one of her mother's ladies-in-waiting, Lady Flora Hastings, developed an abdominal growth that was widely rumoured to be an out-of-wedlock pregnancy by Sir John Conroy.[41] Victoria believed the rumours.[42] She hated Conroy, and despised "that odious Lady Flora",[43] because she had conspired with Conroy and the Duchess of Kent in the Kensington System.[44] At first, Lady Flora refused to submit to a naked medical examination, until in mid-February she eventually agreed, and was found to be a virgin.[45] Conroy, the Hastings family and the opposition Tories organised a press campaign implicating the Queen in the spreading of false rumours about Lady Flora.[46] When Lady Flora died in July, the post-mortem revealed a large tumour on her liver that had distended her abdomen.[47] At public appearances, Victoria was hissed and jeered as "Mrs. Melbourne".[48] In 1839, Melbourne resigned after Radicals and Tories (both of whom Victoria detested) voted against a Bill to suspend the constitution of Jamaica. The Bill removed political power from plantation owners who were resisting measures associated with the abolition of slavery.[49] The Queen commissioned a Tory, Sir Robert Peel, to form a new ministry. At the time, it was customary for the prime minister to appoint members of the Royal Household, who were usually his political allies and their spouses. Many of the Queen's Ladies of the Bedchamber were wives of Whigs, and Peel expected to replace them with wives of Tories. In what became known as the bedchamber crisis, Victoria, advised by Melbourne, objected to their removal. Peel refused to govern under the restrictions imposed by the Queen, and consequently resigned his commission, allowing Melbourne to return to office.[50]

By 1836, the idea of marriage between Albert and his cousin, Victoria, had arisen in the mind of their ambitious uncle, Leopold, who had been King of the Belgians since 1831.[13] At this time, Victoria was the heiress presumptive to the British throne. Her father, Edward Augustus, Duke of Kent, the fourth son of King George III, had died when she was a baby, and her childless elderly uncle, William IV, was king. Her mother, the Duchess of Kent, Victoria of Saxe-Coburg-Saalfeld, was the sister of both Albert's father—the Duke of Saxe-Coburg and Gotha—and Leopold, King of the Belgians. Leopold arranged for his sister, Victoria's mother, to invite the Duke of Saxe-Coburg and Gotha and his two sons to visit her in May 1836, with the purpose of meeting Victoria. King William IV, however, disapproved of any match with the Coburgs, and instead favoured the suit of Prince Alexander, second son of the Prince of Orange. Victoria was well aware of the various matrimonial plans and critically appraised a parade of eligible princes.[14] She wrote, "[Albert] is extremely handsome; his hair is about the same colour as mine; his eyes are large and blue, and he has a beautiful nose and a very sweet mouth with fine teeth; but the charm of his countenance is his expression, which is most delightful."[15] Alexander, on the other hand, was "very plain".[15] Victoria wrote to her uncle Leopold to thank him "for the prospect of great happiness you have contributed to give me, in the person of dear Albert ... He possesses every quality that could be desired to render me perfectly happy."[16] Although the parties did not undertake a formal engagement, both the family and their retainers widely assumed that the match would take place.[17] Victoria came to the throne aged just eighteen on 20 June 1837. Her letters of the time show interest in Albert's education for the role he would have to play, although she resisted attempts to rush her into marriage.[18] In the winter of 1838–39, the prince visited Italy, accompanied by the Coburg family's confidential adviser, Baron Stockmar.[19] Albert returned to England with Ernest in October 1839 to visit the Queen, with the object of settling the marriage.[20] Albert and Victoria felt mutual affection and the Queen proposed to him on 15 October 1839.[21] Victoria's intention to marry was declared formally to the Privy Council on 23 November,[22] and the couple married on 10 February 1840 at the Chapel Royal, St. James's Palace.[23] Just before the marriage, Albert was naturalised by Act of Parliament,[24] and granted the style of Royal Highness by an Order in Council.[1] At first, he was not popular with the British public. He was perceived to be from an impoverished and undistinguished minor state, barely larger than a small English county.[25] The British Prime Minister, Lord Melbourne, advised the Queen against granting her husband the title of "King Consort". Parliament even refused to make Albert a peer—partly because of anti-German feeling and a desire to exclude Albert from any political role.[26] Melbourne led a minority government and the opposition took advantage of the marriage to weaken his position further. They opposed the ennoblement of Albert and granted him a smaller annuity than previous consorts,[27] £30,000 instead of the usual £50,000.[28] Albert claimed that he had no need of a British peerage; he wrote, "It would almost be a step downwards, for as a Duke of Saxony, I feel myself much higher than a Duke of York or Kent".[29] For the next seventeen years, Albert was formally titled "HRH Prince Albert" until, on 25 June 1857, Victoria formally granted him the title Prince Consort.[30]

Following a custom she maintained throughout her widowhood, Victoria spent the Christmas of 1900 at Osborne House on the Isle of Wight. Rheumatism in her legs had rendered her lame, and her eyesight was clouded by cataracts.[187] Through early January, she felt "weak and unwell",[188] and by mid-January she was "drowsy ... dazed, [and] confused".[189] She died on Tuesday 22 January 1901 at half past six in the evening, at the age of 81.[190] Her son and successor King Edward VII, and her eldest grandson, Emperor Wilhelm II of Germany, were at her deathbed.[191] Her favourite pet Pomeranian, Turri, lay upon her deathbed as a last request.[192] In 1897, Victoria had written instructions for her funeral, which was to be military as befitting a soldier's daughter and the head of the army,[95] and white instead of black.[193] On 25 January, Edward VII, the Kaiser and Prince Arthur, Duke of Connaught, helped lift her into the coffin.[194] She was dressed in a white dress and her wedding veil.[195] An array of mementos commemorating her extended family, friends and servants were laid in the coffin with her, at her request, by her doctor and dressers. One of Albert's dressing gowns was placed by her side, with a plaster cast of his hand, while a lock of John Brown's hair, along with a picture of him, were placed in her left hand concealed from the view of the family by a carefully positioned bunch of flowers.[95][196] Items of jewellery placed on Victoria included the wedding ring of John Brown's mother, given to her by Brown in 1883.[95] Her funeral was held on Saturday 2 February in St George's Chapel, Windsor Castle, and after two days of lying-in-state, she was interred beside Prince Albert in Frogmore Mausoleum at Windsor Great Park. As she was laid to rest at the mausoleum, it began to snow.[197] Victoria is the longest-reigning British monarch and the longest-reigning queen regnant in world history; she reigned for a total of 63 years, seven months and two days. She was the last monarch of Britain from the House of Hanover. Her son and heir Edward VII belonged to her husband's House of Saxe-Coburg and Gotha.