This article covers the history of London in the 19th century.

During the 19th century, London was transformed into the world's largest city and capital of the British Empire. Its population expanded from 1 million in 1800 to 6.7 million a century later (1.9% average annual growth). During this period, London became a global political, financial, and trading capital. In this position, it was largely unrivaled until the latter part of the century, when Paris and New York City began to threaten its dominance.

While the city grew wealthy as Britain's holdings expanded, 19th century London was also a city of poverty, where millions lived in overcrowded and unsanitary slums. Life for the poor was immortalized by Charles Dickens in such novels as Oliver Twist.

One of the most famous events of 19th-century London was the Great Exhibition of 1851. Held at The Crystal Palace, the fair attracted visitors from across the world and displayed Britain at the height of its Imperial dominance.

As the capital of a massive empire, London became a magnet for immigrants from the colonies and poorer parts of Europe. A large Irish population settled in the city during the Victorian era, with many of the newcomers refugees from the Great Famine (1845-1849). At one point, Irish immigrants made up about 20% of London's population. London also became home to a sizable Jewish community, and small communities of Chinese and South Asians settled in the city

London ⁱ/ˈlʌndən/ is the capital city of England and the United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its founding by the Romans, who named it Londinium. London's ancient core, the City of London, largely retains its square-mile mediaeval boundaries. Since at least the 19th century, the name London has also referred to the metropolis developed around this core. The bulk of this conurbation forms the London region and the Greater London administrative area, governed by the elected Mayor of London and the London Assembly.

London is a leading global city, with strengths in the arts, commerce, education, entertainment, fashion, finance, healthcare, media, professional services, research and development, tourism and transport all contributing to its prominence. It is the world's leading financial centre alongside New York City and has the fifth-largest city GDP in the world (and the largest in Europe). London has been described as a world cultural capital. It was the world's most visited city during 2011 and London Heathrow is the world's busiest airport by number of international passengers. London's 43 universities form the largest concentration of higher education in Europe. In 2012 London will become the first city to host the modern Summer Olympic Games three times.

The 19th century (1801–1900) was a period in history marked by the collapse of the Spanish, Portuguese, First and Second French, Chinese, Holy Roman and Mughal empires. This paved the way for the growing influence of the British Empire, Russian Empire, German Empire, the United States and the Empire of Japan, spurring military conflicts but also advances in science and exploration.

After the defeat of the French Empire and its allies in the Napoleonic Wars, the British Empire became the world's leading power, controlling one quarter of the world's population and one fifth of the total land area. It enforced a Pax Britannica, encouraged trade, and battled rampant piracy. The 19th century was an era of invention and discovery, with significant developments in the fields of mathematics, physics, chemistry, biology, electricity, and metallurgy that lay the groundwork for the technological advances of the 20th century. The Industrial Revolution began in Europe. The Victorian era was notorious for the employment of young children in factories and mines. In Japan, after the Meiji Restoration, Japan embarked on a program of rapid modernization. Then Japan went to war against Qing-ruled China, and won the First Sino-Japanese War.