The story takes place in September 1949, mainly at sea in the Straits of Florida, an ocean passage between Florida and Cuba that separates the Gulf of Mexico to the west and the Atlantic Ocean to the east. Several times in the story, Santiago thinks about an ocean current that carries him and the hooked marlin eastward; this is the Florida Current, which flows through the Straits and forms the beginning of the Gulf Stream that travels up the US east coast and across the Atlantic toward Great Britain.

At one point, a plane flies overhead on its way from Havana to Miami in Florida. From the Spanish-American War of 1898 until the Cuban Revolution of 1959, Cuba was nominally independent but heavily influenced by the US. During the late 1940s, a weak democracy controlled Cuba, whose middle class prospered in an economy bolstered by tourism, sugar cane, and tobacco, but a large portion of the citizenry was poverty stricken. Santiago is part of that population: He wishes he had a radio to keep him company during his fishing expedition, and he pretends, with the boy Manolin, that he eats well at night.