British Airways and Latvian carrier Air Baltic have signed a codeshare agreement.
The deal allows BA customers to book tickets from London Gatwick to Riga on Air Baltic for travel from September 23.
BA Executive Club members will be able to earn Avios points on the route.
The agreement also opens up the BA network to Air Baltic passengers.
Keith Williams, BA's executive chairman, said: "The addition of Riga to our route network is fantastic news for our customers and we look forward to working with airBaltic to introduce the delights of Latvia to a wider audience."
Air Baltic, which is not a member of an airline alliance, operates ten weekly services to Riga in the summer season and seven in the winter. It serves more than 60 destinations from Riga.
Martin Gauss, CEO of Air Baltic, said: "Riga to London is by far the most popular city-pair for travellers starting or finishing their journey in the Baltic region. We are very pleased to add British Airways, the UK's largest international airline and one of the world's leading global premium carriers, to our growing family of codeshare partners."
Last month, BA added its flight code to a further nine Vueling services (see news, August 12).