Guillermo Brown Blanco was married to Corina Caravia Gutiérrez, daughter of Bernabé Caravia Pérez and Dolores Gutiérrez Bosch, belonging to a traditional Uruguayan family. He and his wife were the parents of Guillermo Brown Caravia, a prominent officer of the Argentine Navy. His paternal and maternal grandparents were William Brown and Juan Benito Blanco Farías, a politician who participated in the War of Independence.