British Airways and its Paris-based subsidiary Open Skies have signed an interline agreement with French carrier Corsair.
Corsair and Open Skies are both based at Paris' Orly airport.
Open Skies operates to New York's two main airports, while Corsair has a range of routes to former French dependencies including Senegal and the Ivory Coast plus Reunion, Mauritius and Madagascar. BA offers flights to Heathrow from Orly.
The deal applies regardless of the direction of travel.
A spokesman said: "With this bilateral agreement, customers can for example take a flight from the island of Reunion to London or New York with a single ticket."
The interline agreement is particularly aimed at the large number of travellers from Reunion. The airlines claim that the price of a straight through ticket from here will be less than two purchased separately.
Gary Noakes