Under the British, Mauritius was no longer a free port. To compensate for the resulting loss in trade, the government encouraged sugar production. In 1825 Britain equalized the duty on sugar from all of its colonies, providing a strong stimulus for Mauritians to produce more sugar. Production leaped from 11,000 tons in 1825 to 21,000 tons in 1826; by 1854 production exceeded 100,000 tons. By the mid-nineteenth century, Mauritius had reached the apex of its importance in the world sugar market: it was Britain's main sugar-producing colony and produced 9.4 percent of the world's sugarcane between 1855 and 1859. Although overall production would continue to rise into the twentieth century, declines in world prices and a massive increase in production in other countries robbed Mauritius of its dominant role in subsequent years. Nonetheless, as sugar increased in economic importance, the percentage of food crop production dropped accordingly, and landownership became concentrated in large, profitable estates.

Indentured workers from India replaced slaves as a source of cheap labor for the sugar plantations. Between 1834 and 1910 (the last year of arrivals), 451,776 Indians migrated to Mauritius, the majority arriving before 1865. Because 157,639 of these Indians left, the island had a net gain of 294,137 Indians during the period. Most workers came from Bengal and Madras, under contract to work for at least ten years for low wages under harsh conditions. At the end of their contracts, workers supposedly had the option of returning home, but plantation owners often succeeded in eliminating this choice. Many plantation owners punished workers with beatings, hunted down those who ran away and imprisoned them, and unjustly withheld pay. In 1878 a labor law regularized the pay system, and in 1917 the indenture system formally ended. Moreover, a 1922 law permitted workers to choose their places of work.

By 1871 more than 68 percent of the population was Indian, of which more than 25 percent had been born in Mauritius. In 1931 the proportion of Indians in the population was the same, but more than 93 percent of them were natives. By contrast, Mauritius had no immigration from Africa. The freed slaves and their Creole offspring left the plantations to become fishers, dockworkers, and civil servants and formed about 20 percent of the population in 1931. A number of Chinese immigrated during the nineteenth century, and this group made up about 2 percent of the population in 1931. The Indian rupee became the island's official currency in 1876.

Starting in the 1860s, the island's sugar economy declined in the face of varied pressures. As sugar beet production and sugarcane production in other countries increased, world prices declined. The opening of the Suez Canal in 1869 shifted trade routes away from the Indian Ocean. And, in addition to regularly occurring droughts and cyclones, a deadly malaria epidemic killed more than 40,000 people between 1867 and 1869. The FrancoMauritian plantation owners responded in several ways. They cut costs by centralizing sugar production in fewer factories. Furthermore, to increase the profitability of their operations, from the 1870s to about 1920 the planters sold the less productive portions of their landholdings. The process was known as the grand morcellement, and it permitted many Indians who could put together enough capital to become small landowners. This meant that for the first time, sugar was produced on small plots with free labor. Between 1864 and 1900, according to one scholar, Indians purchased 24 million rupees worth of land. By 1921 Indians owned about 35 percent of the island's cultivated land.

Data as of August 1994