The new route will be the airline’s lengthiest with a flight time of 14 hours 40 minutes.
BA will use one of its new Boeing 787 Dreamliners on the route, which will run four-times-a-week from January 3, 2017.
Santiago is the latest Latin American destination for the airline, and joins the recently launched services to San Jose in Costa Rica and Lima in Peru. In addition, it also operates flight to Rio and Sao Paulo in Brazil and Buenos Aires in Argentina.
Alex Cruz, chairman and chief executive of British Airways, said: “In recent years we have been increasing our services to South and Central America reflecting the area’s continued growth in both business and tourism.
“This year we’ve already launched flights to Costa Rica and Peru, and the addition of Santiago will secure another important link between the UK and the region.”