He was ordained as a priest in 1870 and one year later he moved to Morocco, filling the office of superior in Casablanca and Tangier. In 1883, he returned to Spain and founded Vistahermosa Convent.
Francisco Mª Saco wrote some opuscules and several articles such as Estatutos Municipales de la Venerable Orden Tercera de Penitencia... de la ciudad de Tánger (1881), Estatutos de la Santa Provincia de Santiago (1883) and Las misiones franciscano-españolas en Marruecos (1876).