Inspired on the flag of the Oriental Province with an added motto it was first used in 1825 in the military expedition of the Treinta y Tres Orientales meant to free the country from Brazilian occupation.

The flag of the Treinta y Tres pays homage to the military expedition of the Treinta y Tres Orientales ('Thirty-Three Orientals'), an insurgent revolutionary group led by Juan Antonio Lavalleja and Manuel Oribe which fought against the Empire of Brazil during the Brazilian occupation of the Provincia Oriental.

The flag was first used during the disembarkation of the Thirty-Three Orientals in Uruguayan territory on 19 April 1825, at the beginning of the Cisplatine War.

The design features three horizontal stripes: the top stripe, blue, represents greatness; the center one, white, is a symbol of the Republic; and the bottom one, red, honors the blood of those who died for freedom and independence.

Uruguay's national motto Libertad o Muerte ("Freedom or Death") reads on the center stripe.