Between 1865 and 1867, Acosta was a member of a Puerto Rican commission, which included Segundo Ruiz Belvis and Francisco Mariano Quiñones, and which participated in the Junta Informativa de Reformas de Ultramar (Overseas Reforms Informative Board) which met in Madrid. Here, Acosta presented the argument for the abolition of slavery in Puerto Rico. That same year, whilst in Madrid, Acosta was made a member of the Spanish Royal Academy of History, for his work in the editing of Fray Iñigo Abbad y Lasierra's Historia geografica, civil y natural de la isla de San Juan Bautista de Puerto Rico. (Geographic, Civil, and Natural History of the Island of St. John the Baptist of Puerto Rico)