Born in Buenos Aires, he initially studied law, but abandoned his studies in favor of politics. In 1839, no sooner had he begun to make a name for himself than he was arrested for his opposition to Argentina's conservative caudillo, Juan Manuel de Rosas. He was held in irons for six days. A year and a half later, the political climate spurred him, as it had many other Argentine dissenters, to flee the country. He found passage to Montevideo on a French schooner. He was welcomed by other exiles, among them Juan Bautista Alberdi, Florencio Varela, Esteban Echeverría, Juan María Gutiérrez, and Miguel Cané. Three years later, the siege of Montevideo by Rosas's ally Manuel Oribe led Mármol to flee yet again, this time to Rio de Janeiro. Here he remained until February 1843, at which point he boarded a ship for Chile. The ship encountered fierce storms and was eventually forced to return to Rio de Janeiro. He remained in the city another two years before returning to Montevideo, where he spent the next seven years.