The 3 September 1843 Revolution (N.S. 15 September) was an uprising by the Hellenic Army in Athens, supported by large sections of the population, against the autocratic rule of King Otto. The rebels, led by veterans of the Greek War of Independence, demanded a constitution and the departure of the Bavarian officials who dominated the government. The revolution succeeded, ushering in a period of constitutional monarchy (under the 1844 constitution) and universal suffrage in Greece.

Background: During the War of Independence, the Greek rebels had passed a series of liberal and progressive constitutions on which the war's provisional governments were based. With the establishment of the monarchy in 1832 and the arrival of the Bavarian prince Otto as king, however, these liberal institutions were discarded. For the next ten years, Otto and his mainly Bavarian officials ruled in an autocratic manner, causing widespread resentment among a people who had just been liberated from foreign rule. The "Bavarocracy" (Βαυαροκρατία), as it was called—intentionally recalling the periods of "Francocracy" and "Turkocracy"—even extended to the use of German alongside Greek in the state administration. Greek politicians constantly demanded an end to this state of affairs. They wanted the Bavarians, above all the much‑despised Major Hess, sent back to their country and a constitution to be granted. However, they did not question the monarchy itself or the power of the king. Indeed, they did not wish to impose a constitution but demanded that the king grant them one. These demands grew ever stronger as time passed and cut across the political spectrum: the French, English, and Russian parties all voiced them. The king's repeated refusals to yield led to radicalization. Therefore, the politicians resorted to conspiracy, which was not a new form of political action in Greece — it had preceded and occurred during the War of Independence. The first Greek governments, such as that of John Capodistria, had to confront conspiracies, which had never really disappeared. However, this movement was much more important and came out into the open on 3 September 1843. The principal conspirators were Yannis Makriyannis, Andreas Metaxas, Andreas Londos, and Michael Soutzos. They had managed to convince certain officers to join their side, chief among them Colonel Dimitrios Kallergis (commander of the Athens cavalry), Colonel Nikolaos Skarvelis (commander of the Athens infantry), and Colonel Spyromilios (commander of the Military Academy). Thus, the conspirators were certain to have army support. Their idea was to act quickly to present the palace with a fait accompli. A first date was chosen: 25 March 1844, the anniversary of the uprising against the Ottomans. The constitution thus appeared as the logical and necessary consequence of independence, but the conspiracy was poorly kept. Yannis Makriyannis, for example, spent his time recruiting new conspirators and in the process exposed the plot. It was decided to move more quickly to action at the beginning of September 1843.

On the night of 2 September 1843 it was learned that the names of the conspirators were known to the police, and incidents took place around Makriyannis's home. Kallergis therefore acted on his own initiative: he went to the barracks, gathered his men, and headed for the Old Royal Palace. At the same time he ordered the gates of the Medrese Prison to be opened. Captain Schinas, commander of the Athens artillery, received orders to suppress the nascent insurrection but chose to join the movement. The soldiers arrived at the Old Royal Palace and shouted "Long live the Constitution!" beneath the king's windows. Otto yielded to the demands and granted the 1844 Constitution; the Council of State had already prepared the constitution in anticipation of the coup. The king then asked Metaxas to form a new government and to summon a new National Assembly, which met on 10 November (OS) / 20 November (NS). The troops returned to their barracks, acclaiming the king as a constitutional monarch. The coup was bloodless, and France and the United Kingdom accepted these changes without difficulty. For the French of the July Monarchy era, 3 September 1843 recalled their Revolution of 1830. For the British, the Glorious Revolution of 1688 remained the liberal model par excellence in the nineteenth century. Only Russia condemned the movement because of its autocratic, authoritarian, and consequently anti‑liberal nature. The assembly designated a constitutional commission, and a constitution was proclaimed in March 1844. Since then, the square in front of the Old Royal Palace has been renamed Constitution Square (Syntagma Square in Greek).

Brunet de Presle and A. Blanchet, La Grèce depuis la conquête romaine jusqu'à nos jours, Firmin Didot, Paris, 1860.