The Assembly of the Year XIII, (Spanish: Asamblea del Año XIII) also known as the General Constituent and Sovereign Assembly of the Year 1813 (Asamblea General Constituyente y Soberana del Año 1813), was a congress of deputies of the United Provinces of the Río de la Plata convened by the Second Triumvirate, which met in Buenos Aires from 31 January 1813 to 24 January 1815. Its objectives were for the representatives of the "free peoples" to recognise the sovereignty of the people, proclaim the independence of the United Provinces and draft a constitution that would define the institutional system of the new state. Although these last two objectives were not met, the assembly established a significant number of reforms in the Rioplatense institutions and among other measures established the celebration of 25 May as a civic holiday, remove the image of Ferdinand VII from coins and official documents, declared the principle of the sovereignty of the people, commissioned the composition of a national anthem, dictated the abolition of slavery, removed nobility titles, and proclaimed freedom of the press among other things.

In order to constitute the Assembly of the Year XIII, the Second Triumvirate quickly decreed on 24 October 1812 the number of deputies that would correspond, according to their importance, to the capital —Buenos Aires—, to the capitals of each province or intendancy, and to each dependent city, with the exception of San Miguel de Tucumán, which elected two deputies as a reward for the recent victory over the royalist army.

Article 6. This Capital shall have four Deputies due to its greater population and political importance; the other Provincial Capitals shall appoint two, and one for each city under their jurisdiction, except for Tucumán, which may at its discretion attend the Assembly with two Deputies.
Decree calling elections (trans-title=Decree calling elections for the Assembly of the Year XIII)

In compliance with the decree of the triumvirs, the following deputies were elected in the territory of the Provinces of the Río de la Plata:

The deputies representing the provinces of Upper Peru were elected under the protection of the Auxiliary Army and the republiquetas. On 29 July 1813, a peremptory circular was sent to the governors-intendant of Potosí and Cochabamba, the president of Charcas, and the lieutenant governors of Santa Cruz de la Sierra and Tarija to accelerate the election of deputies, ordering General Manuel Belgrano to enforce it.

They failed to join the assembly:

On 5 March 1813, the Assembly suspended the incorporation of the deputies from the Banda Oriental, elected on 21 April 1813 at the "Congress of Tres Cruces" under the leadership of José Gervasio Artigas, expressing doubts about the lack of formal procedure in the election. Only two deputies had been elected by the cabildos as ordered; the rest were chosen by the provincial congress meeting in Tres Cruces. Traditional Uruguayan historiography considers that the reason was the refusal to incorporate deputies arriving with the instructions proposed by Artigas, aimed at immediately declaring independence from the Kingdom of Spain and organizing the provinces under a confederal state, which broke with the existing centralization. The six Oriental deputies corresponded to the six cabildos of the province:

The Assembly sent deputy Pedro Pablo Vidal to negotiate with Artigas, but no agreement was reached, and in the session of 1 June 1813, confirmed on the 11th of the same month after a request for review, most of the Oriental deputies were rejected. Exempted from this measure were the two deputies elected according to the prescribed method before the Congress of Tres Cruces: that of Maldonado, Dámaso Gómez Fonseca —resident in Buenos Aires— and that of Montevideo, Dámaso Larrañaga. However, only the former joined, as the latter did not travel to Buenos Aires and instead extended powers to his replacement, Artigas' envoy Tomás García de Zúñiga, who in turn withdrew the request for incorporation.