The Mejba Revolt (1864–65) was a rebellion in Tunisia against the doubling of an unpopular poll tax (the mejba) imposed on his subjects by Sadok Bey. The most extensive revolt against the rule of the Husainid Beys of Tunis, it saw uprisings all over the country and came close to prompting military intervention by Britain and France. The revolt was suppressed with great brutality and the government became ever more seriously indebted to foreign creditors, backed by European governments, until it was finally unable to resist French occupation in 1881.

Public debt did not exist in the Regency of Tunis until the end of the reign of Mustapha Bey in 1837, but his successors found themselves in increasingly difficult financial circumstances. They wanted to modernise the country and its institutions: Ahmed Bey had set up a military academy at Le Bardo and begun training a larger army. He sent 15,000 Tunisian soldiers to fight for the Ottoman Empire in the Crimean War, and also established new government offices—the rabta managing state grain silos; the ghaba in charge of olive oil forests; and the ghorfa, the central state procurement office. His successor Muhammad Bey was an ambitious palace-builder.

To fund these expensive new ventures, the Beys of Tunis relied on tax revenues paid on a customary basis. Most of the country paid the mejba (Arabic: مجبة) established in the seventeenth century under the Muradid dynasty. There is much scholarly debate about exactly what this constituted and how it was levied, but it appears that before 1856, the term mejba signified a tax paid by a tribe, clan or other social group, based on a collective assessment. The Beys also imposed monopoly taxes on salt, tobacco, tanned hides and other commodities.

In 1856, Muhammad Bey embarked on a major fiscal reform. He gave up most of his taxes on commodities and agricultural goods (except for olive and date trees, oils and cereals) as well as the old mejba levies, and instituted a new capitation tax called the i'ana (Arabic: اعانة) which quickly also became known as the mejba, although it was a new tax calculated on a completely different basis—it was levied on individuals rather than on groups. This new mejba was fixed at 36 piastres per adult male per year. For most peasants, this equated to about 45 days' labour. To reduce potential unrest, the five largest towns—Tunis, Sfax, Sousse, Monastir, Tunisia and Kairouan—were exempted. The new tax raised 9.7m piastres out of a total 22.95m piastres of government income. Although burdensome, the new mejba was not sufficient to eliminate the government deficit. The developing economy meant that increasingly gold and silver coin tended to fall into the hands of European merchants, who took it out of the country. When the foreign merchants refused to accept copper coins, Muhammad Bey issued debased currency in 1858.

Since the beginning of the conquest of Algeria in 1830, France had maintained a close interest in the affairs of the Regency, and successive Beys had sought to avoid giving France or any other power reason to intervene further. However the Batto Sfez Affair in 1857 did give France an excuse to put more pressure on Muhammad Bey, and a naval squadron of nine ships and seven hundred cannon was sent to La Goulette to insist that he promptly adopt a series of reforms modelled on the Ottoman Tanzimat. As a result, Muhammad Bey agreed to the Fundamental Pact (Arabic: عهد الأمان) ('Ahd al-Aman or Pledge of Security). The Pact guaranteed equality of taxation (thus implicitly abolishing the discriminatory jizya tax imposed on non-Muslims). It also permitted foreigners to own land, participate in all types of businesses and set up separate commercial courts. A number of concessions were quickly granted to French firms, for example to construct telegraph lines and renovate the Zaghouan aqueduct. The Fundamental Pact thus further undermined the shaky finances of the Regency by abolishing traditional taxes, and opened the door to commercial penetration of the country by foreign business. Both issues were to become points of grievance in the Mejba Revolt.

Muhammad Bey was succeeded in 1859 by his brother Sadok Bey, In 1860, Sadok Bey introduced conscription for the first time in Tunisia—military service was now obligatory for a period of eight years. Recruits were selected by lot, and those who could afford it could buy themselves out of the service. Thus it was only the poor who ended up serving.

Following the introduction of the new mejba and military service, on 23 April 1861 Sadok Bey promulgated the first written constitution in the Arab world, separating executive, legislative and judiciary powers, through a new Supreme Council, legislature and court system and thereby limiting his own powers. This constitution reaffirmed the equality of rights for Muslims, Christians (effectively, therefore, for Europeans) and for Jews; in particular, concerning the right to own property. This created a new legal environment which encouraged Europeans to set up businesses in Tunisia. The new constitution was not popular. The new Supreme Council was filled with placemen of the Prime Minister Mustapha Khaznadar, mamluks, and others of Turkish and non-native descent, with few of the traditional Arab tribal leaders of the interior. The customary links between ruler and ruled were displaced, and it became harder for the sheikhs outside Tunis to gain audience. The costs of the new institutions were regarded as excessive, and resented as a sign of foreign interference.

Sadok Bey tried to resolve the country's chronic financial problems in May 1862 by borrowing 10m piastres at 12% interest from Nassim Shamama, his Jewish Receiver-General of Finances. As a result, internal public debt increased by 60% during the first three years of his reign.