The Great Council or Major Council (Italian: Maggior Consiglio; Venetian: Mazor Consegio) was a political organ of the Republic of Venice between 1172 and 1797. It was the chief political assembly, responsible for electing many of the other political offices and the senior councils that ran the Republic, passing laws, and exercising judicial oversight. Following the lockout (Serrata) of 1297, its membership was established on hereditary right, exclusive to the patrician families enrolled in the Golden Book of the Venetian nobility.

The Great Council was unique at the time in its usage of lottery to select nominators for proposal of candidates, who were thereafter voted upon.

The exact origins of the Great Council are unclear. Tradition places its establishment in 1172, but it likely has its origin in a 'Council of Wise Men' (Consilium Sapientium) that is attested in 1141. That was a council established to limit and control the power of the Doge of Venice, and dominated by the Venetian nobility.

The Great Council superseded the general assembly of the people (the Concio or Arengo), which was convened only to ratify laws and elect a new Doge. Its role was to elect all magistracies, approve laws, as well as exercise judicial functions including the granting of pardons. However, as the Great Council itself was too large and unwieldy, numbering some 300–400 members already in the 13th century, the actual deliberation and decision-making of government took place in smaller councils, more capable of action. In the 13th century, the most important of these was the Council of Forty, which not only served as the supreme judicial body, but also prepared legislation to be submitted to the Great Council. Its three heads (the capi), along with the six ducal councillors, and the Doge, constituted the Signoria of Venice.

In its early days, the Great Council was a relatively open and democratic institution, its membership being in theory open to the entire body of free citizens. Members were nominated by three electors, though it is unclear how these were chosen; they were selected partly by lot and partly by rotation. In 1230, the electoral process was altered for unknown reasons, with seven electors serving between 29 September and 29 March, and three during the other six months. However, it appears that the number of electors fluctuated, and could be as small as four.

These electors chose one hundred members to be nominated for election to the next year's Great Council, but since there was no alternate slate of candidates, the names chosen were also elected. The "somewhat haphazard" election process placed enormous power on the hands of the very few electors, who were constrained only by force of custom to not abuse their position. In addition, certain office-holders, such as the ducal councillors or members of the Council of Forty, were members ex officio, and they outnumbered the elected members by a considerable margin. As the historian Frederic C. Lane puts it, "one can say that the Great Council contained all the most important people who were available in Venice and a sprinkling of others named to it because someone thought they were potentially important".

As the Great Council elected people to the various offices of the Venetian government, it "had become the gatekeeper for power and prestige in Venice". During the 13th century, this gave rise to a political struggle between reformers, who wanted to open membership to the Great Council, and thus to the political elite, up to newcomers, and conservatives, who wished to preserve the patriciate's dominance.

While the names of noble families predominate during the 13th century, commoners were still included in the rolls. But even among the nobility there were dissensions. A rising population and wealth meant that more and more citizens sought admission to the Great Council, but the traditional patrician families of the Rialto resisted the addition of these nouveau riche to the Council. Likewise complicated was the issue of foreigners, nobles from Venice's nascent colonial empire in the East or from Dalmatia, or Venetian expatriate families returning to the metropolis after decades of absence, due to the fall of the Crusader states in the Levant in the late 13th century. These men were counted as Venetian citizens, but were culturally foreign to the mother city.