Oneworld partners British Airways and TAM Airlines will begin a codeshare agreement next month.
The agreement covers flights between London Heathrow and Sao Paulo "and beyond".
BA's code will be added to TAM's London Heathrow-Sao Paulo service, allowing the UK carrier's passengers to book seats on TAM's daily flight.
TAM passengers will be able to book onward connections on BA domestic routes with a single booking.
TAM's code will not be added to BA's daily service between LHR and Sao Paulo and the codeshare does not extend to BA passengers through-booking with TAM to local destinations in South America.
However, BA said it "hopes to expand this relationship in the coming months".
Members of BA's Executive Club and TAM's Fidelidade will be able to earn points and redeem tickets when flying on the partner airline.
Sean Doyle, BA's head of alliances and joint business, said: "We are very pleased to be working more closely with TAM, our Oneworld partner, and offer our customers more choice when flying to Brazil."
Claudia Sender, CEO of TAM SA, added: "It's an honour to have British Airways as our partner. This agreement adds important destinations in the UK to our network, further extending the connectivity for our passengers."
Earlier this week, BA announced it will open a Galleries lounge in Dubai International airport's new Concourse D (see news, September 1).