[2][3] Masó, son of a Catalan father and a Cuban-born mother from Bayamo, was born in Yara on a farm named "Cerca Pie"; later he moved with his parents to the coastal city of Manzanillo.

When in 1867 Carlos Manuel de Céspedes, Francisco Vicente Aguilera and other began to conspire ways to look at the independence of Cuba, Masó was one of the first who joined the cause.

On 10 October 1868, when he thought the moment had come and took off with his two brothers, he met Céspedes in La Demajagua and took part in the unsuccessful uprising of Yara.

Due to the serious illness of Guillermo Moncada, Masó transferred the command of the rebels in the Oriente until the arrival of major generals Antonio Maceo and Máximo Gómez.

He withdrew his candidacy under pressure from the United States, which secured a permanent right of intervention in the young republic by the Platt Amendment, opposed by Masó.