British Airways is adding its flight code to more than 170 Vueling services.
The codeshare agreement between the two IAG airlines largely centres on the Spanish low-cost carrier's Italy operation.
Among the 37 international and 11 domestic routes from Vueling's Rome Fiumicino base that are new to BA customers are Brindisi, Palermo, Lamezia, Valencia and Nantes.
Other new routes on offer to BA passengers through the codeshare include London Heathrow to Bilbao and La Coruña; Cardiff to Malaga and Alicante; Edinburgh to Barcelona; Paris Orly to Catania (Sicily); Barcelona to Naples; Brussels to Venice; and Copenhagen to Florence.
Further codeshares between BA and Vueling will be added "in the near future".
Steve Ronald, BA's head of alliances, said: "As we forge ever closer relationships with our fellow IAG airlines, Iberia and Vueling, our customers will be able to access all corners of Europe and beyond, with one simple booking on ba.com and the enticement of the collection of reward points for their loyalty."
Fernando Estrada, Vueling's director of strategy, alliances and business development, added: "We are very excited about this agreement with British Airways, which allows us to be more competitive in the market and concretely support the development of the Airport of Rome Fiumicino and tourism in the city of Rome."
Earlier this week, BA unveiled the new cabin interior that will soon be installed across its short-haul fleet (see news, June 16).