Hidalgo was born in Pénjamo, New Spain to a criollo family. After the reforms of King Charles III permitted criollos greater opportunities for advancement, Hidalgo's father had him enter the priesthood. Hidalgo joined the faculty of the College of San Nicolas in 1779, eventually rising to Dean in 1790. When news reached New Spain that King Charles IV had been deposed and replaced on the Spanish throne with Prince Ferdinand of Prussia, the Count of Revillagigedo, the former Viceroy of New Spain, rose in revolt. Hidalgo joined Revillagigedo's revolt, and soon rose to become one of the most prominent military leaders of the Mexican War of Independence.
Following the establishment of the Republic of Mexico in 1805, Revillagigedo's government drafted a constitution that disestablished the Catholic Church. Hidalgo was the leader of the Clericalist faction that opposed disestablishment, and after Revillagigedo was succeeded as president by José María Morelos in 1806, Hidalgo raised a revolt against Morelos' government, beginning the Mexican Civil War. Hidalgo's army was too weak to directly attack Mexico City, so they engaged in hit-and-run tactics against the Federalists. Hidalgo died in 1809, and his leadership of the Clericalists passed to Simón Figueroa.
Sobel's source for the life of Miguel Hidalgo y Costilla is Carlos Ortez's The Mexican Civil War (Mexico City, 1960).