Calderon, who was president from 1994 to 1999 as the reconstruction of the divided country took hold, died around midnight in a hospital in Houston where he was admitted in critical condition with an undisclosed form of cancer.
El Salvador's 1980-1992 civil war, which pitted a U.S.-backed right-wing government against the leftist guerilla Farabundo Marti National Liberation Front (FMLN), claimed some 75,000 lives and left around another 8,000 people missing.
A founder of the powerful, right-wing Nationalist Republican Alliance (Arena), Calderon as president ushered in a string of business-friendly economic reforms including a privatization of the telecoms sector and the pension system.
El Salvador's Supreme Court of Justice in 2016 ordered an investigation into Calderon's fortune on suspicion of illicit enrichment. The former president, who was also mayor of San Salvador between 1988 and 1994, rejected the accusations.