The Septinsular Republic (Greek: Ἑπτάνησος Πολιτεία, romanized: Heptanēsos Politeia; Italian: Repubblica Settinsulare), also known as the Republic of the Seven United Islands, was an oligarchic republic that existed from 1800 to 1807 under nominal Russian and Ottoman sovereignty in the Ionian Islands (Corfu, Paxoi, Lefkada, Cephalonia, Ithaca, Zakynthos or Zante, and Kythira).

The Republic was established after a joint Russo-Ottoman fleet captured the islands and ended a two-year rule by the French Republic. Although the islanders had hoped for complete independence, the new state was granted only autonomy, becoming tributary to the Ottoman Porte, and de facto under Russian domination. Nevertheless, it was the first time that Greeks had been granted self-government since the fall of the last remnants of the Byzantine Empire to the Ottomans in the mid-15th century. In 1807, the republic was ceded to Napoleon's French Empire, but the islands kept their institutions of government. The British gradually took control of the islands from 1809 on, and following the Treaty of Paris, the islands were formally organised into the United States of the Ionian Islands under British protection.

The Ionian Islands (Corfu, Paxoi, Zakynthos or Zante, Kefalonia, Lefkada, Ithaca, and Kythira or Cerigo) along with a handful of exclaves on the Epirote mainland, namely the coastal towns of Parga, Preveza, Vonitsa, and Butrinto, had been Venetian possessions for centuries, thereby becoming the only part of the Greek world to escape conquest by the Ottoman Empire, developing a distinct local culture, and becoming a place of "dynamic interaction between the West and [...] the Greek East", indeed serving as "Greek culture's window on the West", through which Western European ideas and culture were transmitted to the Greek world.

Under Venetian rule, the population of the islands was divided into three classes: the privileged nobility, the urban middle class (cittadini) and the commoners (popolari). The nobility were mostly landowners, and derided mercantile activity, which was left to the urban commercial class; as a result, the latter also came to amass wealth and land, and aspired to join the ruling class. In this contest, the rural peasantry was generally politically marginalized. This medieval social order was upset after the fall of the Republic of Venice in 1797, when the islands came under French control. Shortly after, in the Treaty of Campo Formio, the islands were annexed to the French Republic and organized into three departments. The Republican French were welcomed by the populace, and the radical ideas of the French Revolution were implemented with the abolition of the local nobility, the equality of the social and religious communities (Orthodox, Catholic, and Jewish) and the installation of democratic regimes and local self-government on the islands. The French also created the islands' first public education system, and introduced the first printing press in what is now Greece.

Inevitably, the French presence was resented by the local aristocracy, now deprived of its privileges, while the heavy taxation and anti-clericalism of the French soon made them unpopular with broad sections of the common populace as well. Following the French invasion of Egypt furthermore, the French presence in the Ionian Islands aroused the opposition of the Ottomans and the Russian Empire, allied with the British, as part of the War of the Second Coalition. No less than the Patriarch of Constantinople, Gregory V, issued a proclamation to the Islanders denouncing the "ungodly" French, calling upon them to rise in revolt, and promising, on behalf of the Ottoman Porte, to allow the Islands to choose their own form of government. In autumn 1798, a joint Russo-Ottoman fleet evicted the French from the other islands and finally captured Corfu on 4 March [O.S. 20 February] 1799, while the autonomous Ottoman strongman Ali Pasha of Yanina took the opportunity to seize Butrinto, Preveza, and Vonitsa from the French.

In all the islands they occupied, the Russians at first installed provisional administrations of nobles and businesspeople alike. On 22 March, however, the Russian authorities invited assemblies of the nobles to undertake the governance of the Ionian Islands, thereby restoring the previous status quo. On the next day, the Great Council of Corfu was reconstituted; its very first action was a vote of thanks to the Allied rulers, the Ottoman Sultan, the Russian Emperor, and the British King. In Zakynthos, however, the local noble council preferred to direct its thanks exclusively to the British, an expression of the strong pro-British tendency on the island, due to the close commercial links centred on the currant trade.

On 6 May [O.S. 24 April] 1800, the commanders of the two fleets announced that the Ionian Islands would comprise a single state, governed by a Senate (Γερουσία) in Corfu city, composed of three representatives each from Corfu, Cephalonia, and Zakynthos, two from Lefkada, and one each from Ithaca, Kythira, and Paxoi. The Venetian nobleman Angelo Orio, the last Venetian provveditore of Argostoli, was appointed head of the Senate, and entrusted with the creation of a constitution for the new state. Orio's draft constitution comprised 28 articles and one addendum, and envisaged a thoroughly aristocratic regime, with each island headed by a Great Council composed of the nobles and the upper bourgeoisie. The Great Councils would elect the senators. Each island would retain a local administrative council of six members and a treasury, but a central treasury would exist in Corfu. The Senate was the ultimate executive authority, and its president the head of state. A Small Council of 40 would be elected by the Great Councils of the three largest islands, and would be responsible for justice, the selection of officials, and advising on legislation. Each island's council would have to ratify the laws passed by the Senate. In addition, the use of the Greek language was sanctioned for the first time in the courts. Ushakov also restored the Orthodox Archbishopric of Corfu, which had been abolished in the 13th century by the Angevin rulers of Corfu.

On 21 June 1799, the Senate sent a twelve-member delegation to Constantinople and Saint Petersburg, drawn from the upper classes of each island, to express its gratitude to the Sultan and Tsar and secure recognition of the new state's independence. The delegates were also tasked with producing a draft constitution and submitting it for ratification, as well as press for the restoration of the Islands' maritime and land frontier with the withdrawal of Ali Pasha from Butrinto, Preveza, and Vonitsa. The delegation included Orio, nominated as ambassador to St. Petersburg, and the presidency of the Senate passed to Count Spyridon Georgios Theotokis of the distinguished Theotokis family, who had previously headed the Provisional Municipality under French rule.