Perhaps the most significant turning point in Queen Victoria's life was the death of Prince Albert in December 1861. His death sent Victoria into a deep depression, and she stayed in seclusion for many years, rarely appearing in public. She mourned him by wearing black for the remaining forty years of her life.

Albert's death came suddenly. In November 1861, he contracted typhoid fever. He lay sick in bed for several weeks, finally succumbing to the disease on December 14. He was only forty-two years old. Victoria was devastated. She wrote to her daughter Victoria shortly afterwards: "How I, who leant on him for all and everything—without whom I did nothing, moved not a finger, arranged not a print or photograph, didn't put on a gown or bonnet if he didn't approve it shall go on, to live, to move, to help myself in difficult moments?"

The Queen turned mourning into the chief concern of her existence the next several years. The Prince's rooms in their residences were maintained exactly as he had them when he was alive. Her servants were instructed to bring hot water into his dressing room every day as they had formerly done for his morning shave. She had statues made of him, displayed mementos of his around the royal palaces, and she spent most of her time secluded in Windsor Castle or in Balmoral up in Scotland, where she had formerly spent so many happy times with her husband.

After the first year, her mourning came to be viewed by many in Britain as obsessive, and public unease arose about the Queen's state of mind and the state of the monarchy generally. This unease was aggravated by Victoria's refusal to appear in public except on the rarest occasions. She made her first public appearance only on October 13, 1863, and then only to unveil a statue of Albert at Aberdeen, Scotland. She appeared publicly in London on June 21, 1864, riding out through the streets in an open carriage. She did not personally appear to open Parliament until the 1866 session, and then only reluctantly.

In 1866, Victoria developed a curious relationship with a Scottish servant of her household named John Brown. Brown had been in service to the Queen for several years as a horse attendant, but in the mid-1860s Victoria came to look upon him not so much as a servant as a close friend. Brown was a Scottish highlander who was proud of his heritage. Furthermore, he was rough and informal in his manners, drank frequently, and had a thick Scottish accent. His treatment of the Queen was often surprisingly casual, an attitude which shocked those who saw them together. He was overheard calling her "woman" on at least one occasion.

The Queen, however, adored Brown and spent hours at a time with him. She soon gave him control of her household, including unique access to the Queen. In July 1867, the Queen was scheduled to watch a military review in Hyde Park, but her appearance was canceled by her ministers after she had insisted that Brown stand by her side during the event. The royal children came to resent his closeness to their mother—especially during the Queen's illness in 1870 when Brown was permitted to see her, and her own children were not. Much gossip surrounded their unusual relationship. Some Britons began to refer to the queen, jokingly, as "Mrs. Brown," others said that he was acting as her spiritual medium, continually contacting Prince Albert from the beyond.

Outside the royal palaces during the 1860s, politics were dominated by a popular push for a Second Reform Bill which would expand the voting population and reform parliament along more democratic lines. With the 1865 death of Lord Palmerston—Prime Minister from 1859–1865, and a moderating influence on liberal tendencies in the government—those liberal tendencies gained new force over British politics, and the Second Reform Bill became a reality in 1867.

During Victoria's years of mourning and seclusion she reformed the British Army. By 1870, Victoria abolished the Army's patronage system, which had allowed offices to be purchased and granted as gifts. The call for reform came about partially due to the lessons learned about British military inefficiency during the Crimean War. It was a result of the attention government officials were paying to the major Prussian victories of 1866 against Austria at Sadowa, and later in the decade against the French in the Franco-Prussian War. The Prussian armies were modern, efficient, and powerful, and the British did not wish to lag behind them militarily. The Army Regulation Bill, which was designed to bring about reforms, was rejected in the House of Lords in 1870, and the changes only came about by royal warrant from the Queen. Victoria approved of restricting royal power in the military, as the reform included the subordination of the role of Commander-in-Chief—a royal appointee, Victoria's cousin, the Duke of Cambridge—to below that of the Secretary of State. She was reluctant to go ahead with these reforms, but judged it the right thing to do despite her personal inclinations, which favored royal patronage.