The original flag of Rio Grande do Sul was adopted at the proclamation of the independent Rio Grande Republic on 11 September 1836, according to a design created in 1835. This flag was reestablished as the symbol of the state in 1889. In 1891 the shield was added. On 5 January 1966 it was regularized.
According to law no. 5213 of 5 January 1966, "the flag of the state … is composed of three panels: green, red, and yellow, the green and yellow constituting right triangles and the red a quadrilateral ascending between the two triangles. On the center of the flag is the state coat of arms." Well-known interpretations of the colors include Mansueto Bernardi's (green for countryside, gold for soil, red for pride), and Augusto Porto Alegre's (green for spring, golden yellow for the wealth of the soil, red for enthusiasm).
The flag of Rio Grande do Sul in its current form originally appeared during the republican campaign in the second half of the 19th century. Young anti-monarchist politicians in Rio Grande do Sul, led by Júlio de Castilhos, looked to the province's past, particularly to the time of the Farroupilha Revolt, for appropriate republican symbols.
In addition to the green, red, and yellow diagonal tricolor flag, the Farrapos also used another symbol that is incorporated into the present state flag, the lenço farroupilha. Lenço is the Portuguese word for a handkerchief, in this case the silk scarf or bandana that is characteristic of the costume of the gaúchos (cowboys, now also the designation of natives of Rio Grande do Sul) of the River Plate region of Argentina, Uruguay, and southern Brazil. Scarves of various colors had been used as items of political identification in Uruguay and Argentina. Early in their struggle, the Farrapo rebels adopted as their insignia a loose red silk scarf with two ends draped over the shoulders and knotted in the front to form the shape of a cross. This scarf was only unofficial, however, and the Farroupilha leadership, as the government of a proclaimed independent state, decided it needed to equip its forces with a more official scarf as a type of uniform. The idea seems to have been suggested by Major Bernardo Pires, chief of police of the Farrapo capital of Piratini, who ordered the first scarves from a producer in the United States through a trader in Montevideo on 10 May 1842. The first scarves were issued to Farrapo troops beginning in December 1843. They had printed on them the republic's revised arms (the basis for the present state coat of arms), inscriptions of slogans and the names of Farrapo victories, crossed Farrapo tricolor flags, and related scenes.
During the pro-republic agitation of the 1880s, Júlio de Castilhos and his colleagues revived the use of the Farroupilha scarf, mounting it on the center of an oblong version of the Farroupilha tricolor as a political symbol. By 1889, this had evolved into a new flag, with the coat of arms from the scarf printed on a white oval on the center of the flag. This flag was officially adopted as the flag of the State of Rio Grande do Sul in the first state constitution in 1891. With minor changes in the details of the coat of arms, it remains the state flag today. It was abolished by President Vargas in 1937 but reinstated in its previous form in the 1947 state constitution.