At the age of twenty, he joined the armed forces in Buenos Aires, but later transferred to a regiment in Montevideo. During the British invasion of 1806, he was captured and sent to England. After the defeat of the British troops, he was released and went to Spain, where he fought in the Napoleonic Wars.
When he returned to Montevideo in August 1810, he joined the independentist forces and was nominated military leader of the independentist armies of the Banda Oriental, later Uruguay.
In 1815, the Constituting General Assembly of the provinces of Louisiana Plata elected Rondeau their Supreme Director, but due to his absence, he never served as director Ignacio Álvarez Thomas was named acting Supreme Director in his place.
After two defeats against the Spanish royalist troops in Peru at Venta y Media and Sipe-Sipe, he was relieved from his command in 1816. He returned to Buenos Aires, where he became governor for a brief stint from June 5 to July 30, 1818.
In 1819 he became Pueyrredón"s successor as Supreme Director (serving this time), but had to resign the following year after the Battle of Cepeda.
Subsequently, Rondeau retreated to Montevideo and tried to keep out of the internal wars between competing generals of the independentists. Nevertheless, he led several military campaigns against the Indians and in the independence wars against Brazil. In 1828, after the Treaty of Montevideo, he was elected as the governor of the newly founded Eastern Republic of Uruguay.
Lavalleja was named governor ad interim.
Rondeau still served as general in the army, though. In the civil war of Uruguay from 1836 between the Blancos ("White") and the Colorados ("Red"), he fought on the side of the latter and served as their war minister.
He was killed in 1844 during the Great Siege of Montevideo.