Nicolás Flores de Valdés joined a supply expedition organized in 1693 by Governor Gregorio de Salinas Varona for the missions in Texas. In 1701, when the garrison of San Juan Bautista was established, Flores was the first to enlist. He continued to serve there for fourteen years, first as a private, then as a sergeant, and later as alferez. He married Nicolasa Ximenes y Baldés on May 3, 1707, in Monclova. He joined the Aguayo expedition in 1719 and at the Marqués de Aguayo's request took soldiers from San Antonio de Béxar to help suppress an Indian revolt at Santa Rosa de Nadadores in 1700. He also acted as scout for the expedition and was of great assistance in securing supplies from San Antonio. When Aguayo went to La Bahía del Espíritu Santo, Flores was left in charge of rebuilding the presidio of San Antonio de Béxar, where he remained as captain. He was an able Indian fighter and kept Apache raids at a minimum. With the exception of one interruption in 1724–25, caused by a misunderstanding with the friars of San Antonio de Valero Mission, he retained his command until his death on June 6, 1731.