Greene visited Mexico from January to May 1938 to research and write a nonfiction account of the persecution of the Catholic Church in Mexico, that he had been planning since 1936.[a] The persecution of the Catholic Church was especially severe in the province of Tabasco, under anti-clerical governor Tomás Garrido Canabal. His campaign succeeded in closing all the churches in the state. It forced the priests to marry and give up their traditional garb. Greene called it the "fiercest persecution of religion anywhere since the reign of Elizabeth." He chronicled his travels in Tabasco in The Lawless Roads, published in 1939. In that generally hostile account of his visit he wrote "That, I think, was the day I began to hate the Mexicans" and at another point described his "growing depression, almost pathological hatred ... for Mexico." Pico Iyer has marveled at how Greene's responses to what he saw could be "so dyspeptic, so loveless, so savagely self-enclosed and blind" in his nonfiction treatment of his journey, though, as another critic has noted, "nowhere in The Power and the Glory is there any indication of the testiness and revulsion" in Greene's nonfiction report. Many details reported in Greene's nonfiction treatment of his Tabasco trip appeared in the novel, from the sound of a revolver in the police chief's holster to the vultures in the sky. The principal characters of The Power and the Glory all have antecedents in The Lawless Roads, mostly as people Greene encountered directly or, in the most important instance, a legendary character that people told him about, a certain "whiskey priest", a fugitive who, as Greene writes in The Lawless Roads, "existed for ten years in the forest and swamps, venturing out only at night".
Another of Greene's inspirations for his main character was the Jesuit priest Miguel Pro, who performed his priestly functions as an underground priest in Tabasco and was executed without trial in 1927 on false charges.
In 1983, Greene said that he first started to become a Christian in Tabasco, where the fidelity of the peasants "assumed such proportions that I couldn't help being profoundly moved."
Despite having visited Mexico and published an account of his travels, in the novel Greene was not meticulous about Tabasco's geography. In The Power and the Glory, he identified the region's northern border as the U.S. and its southern border as the sea, when Tabasco's northern border is actually the Bay of Campeche and its southern border is Chiapas to the south.