Karachi continues to be an important financial and industrial centre and handles most of the overseas trade of Pakistan and the central Asian countries. It accounts for a large portion of the GDP of Pakistan and a large proportion of the country's white collar workers. Karachi's population has continued to grow and is estimated to have passed the 20 million mark, although official figures still show a population of around 14.5 million.The current economic boom in Pakistan has also resulted in a new period of resurgence in the economy of Karachi.

The Baloch tribes from Balochistan and Makran established a small settlement of fishing communities,[5] many of whom still inhabit sections of Sindh, and called it Kolachi. The modern port-city of Karachi, however, was developed by authorities of the British Raj in the 19th century. Upon the independence of Pakistan in 1947, the city was selected to become the national capital, and was settled by Muslim immigrants from India, which radically expanded the city's population and transformed the demographics and economy. Karachi has faced major infrastructural and socio-economic challenges, but modern industries and businesses have developed in the city.

The area of Karachi was known to the ancient Greeks by many names: Krokola, the place where Alexander the Great camped to prepare a fleet for Babylonia after his campaign in the Indus valley; 'Morontobara' (probably Manora island near Karachi harbour), from where Alexander's admiral Nearchus set sail; and Barbarikon, a port of the Indo-Greek Bactrian kingdom. It was later known to the Arabs as Debal, the starting point for Muhammad bin Qasim and his army in 712 CE.

The present city started life as a fishing settlement when a Sindhi fisherwoman called Mai Kolachi took up residence and started a family. The village that later grew out of this settlement was known as Kolachi-jo-Goth (Village of Kolachi in Sindhi). By the late 1700s the village was trading across the Arabian Sea with Muscat and the Persian Gulf region. A small fort was constructed for its protection, armed with cannons imported from Muscat. The fort had two main gateways: one facing the sea, known as Kharra Darwaaza (Brackish Gate) and the other facing the Lyari River known as the Mitta Darwaaza (Sweet Gate). The location of these gates correspond to the modern areas of Kharadar (Khārā Dar) and Mithadar (Mīṭhā Dar).

Karachi was made the capital of Sind in the 1840s. On Napier's departure it was added along with the rest of Sindh to the Bombay Presidency. The British realized the importance of the city as a military cantonment and as a port for exporting the produce of the Indus River basin, and rapidly developed its harbour for shipping. The foundations of a city municipal government were laid down and infrastructure development was undertaken. New businesses started opening up and the population of the town began rising rapidly.

In 1857, the First Indian War for Independence broke out in the subcontinent and the 21st Native Infantry stationed in Karachi declared allegiance to rebels, joining their cause on September 10, 1857. Nevertheless, the British were able to quickly reassert control over Karachi and defeat the uprising. Karachi was known as Khurachee Scinde (i.e. Karachi, Sindh) during the early British colonial rule.

By the time the new country of Pakistan was formed in 1947, Karachi had become a bustling metropolis with beautiful classical and colonial European styled buildings lining the city’s thoroughfares. Karachi was chosen as the capital of Pakistan and accommodated a huge influx of migrants and refugees after partition. The demographics of the city changed dramatically but it still maintained cultural diversity as new residents arrived from all parts of India. In 1958, the capital of Pakistan was moved from Karachi to Rawalpindi and then to Islamabad in 1960. This marked the start of a long period of decline in the city, marked by a lack of development. The 1980s and 1990s saw an influx of refugees from the Afghan war into Karachi. Political tensions between the Muhajir groups (descendants of migrants from the partition era) and other groups also erupted and the city was wracked with political and sectarian violence. Most of these tensions have now simmered down.

Karachi is located in the south of Sindh, on the coast of the Arabian Sea. The city covers an area of approximately 3,530 square kilometers (1,363 sq mi), comprised largely of flat or rolling plains, with hills on the western and northern boundaries of the urban sprawl. Two rivers pass through the city: the River Malir which flows from the east towards the south and centre, and the River Lyari, which flows from north to the south west

Located on the coast, Karachi tends to have a relatively mild climate with low levels of average precipitation (approximately 10 inches per annum), the bulk of which occurs during the July-August monsoon season. Winters are mild and the summers are hot, however the proximity to the sea maintains humidity levels at a near-constant high and cool sea breezes relieve the heat of the summer months. Due to high temperatures during the summer (ranging from 30 to 44 degrees Celsius from April to August), the winter months (November to February) are generally considered the best times to visit Karachi. July, December and January have pleasing and cloudy weather when most of the social events, ranging from weddings to charity fundraisers, frequently take place. Tourists and expatriates visit Karachi in these months, Highest recorded is 47.8 °C (118.0 °F) and lowest is 0 °C (32 °F).