BA will offer Royal Brunei passengers domestic connections through Heathrow to various UK regional airports and onwards to mainland Europe.
The two airlines started working together in 2014, with Royal Brunei introducing a non-stop Heathrow-Brunei service last year.
Its passengers will be issued all necessary boarding passes upon check-in, with their bags checked through to their final destination.
Karam Chand, Royal Brunei chief executive, said the deal would extend its reach in the "vital" UK and Europe markets.
Chand added Royal Brunei’s recent addition of Brisbane to its network would provide British travellers a new option when heading to Australia.
Other routes accessible to British passengers include Brunei itself, Kota Kinabalu and Kuching in Borneo, and Ho Chi Minh City in Vietnam.
“As more travellers look to expand their horizons with visits to Asia and Australia, we’re looking forward to introducing our service, generous entertainment options and competitive fares to new customers in Europe," Chand added.
