Other members of the alliance include Air France-KLM, EasyJet, IAG Group and Lufthansa group.
“Norwegian has always believed in healthy competition among airlines to create more choice and lower fares for passengers. But we also firmly believe in an industry where low-cost and network carriers can unite to tackle the many issues we all face together," Norwegian CEO Bjørn Kjos said.
"We are delighted to join Airlines for Europe to add our voice to the important debate about the huge challenges and opportunities our industry faces in the future," he added.
Rumours had been circulating that Norwegian and Ryanair were working on a so-called feeder agreement in which Ryanair's short-distance routes will be slotted in to Norwegian's long-haul routes.
“We have said that we are interested in cooperation with companies that can feed traffic into our long-distance routes, particularly at London Gatwick. Ryanair is an example of an operator that may be relevant for this,” Norwegian spokesman Lass Sandaker-Nielsen told Norwegian financial outlet E24.
The Irish Ryanair transported 7.5 million travellers in January, but the airline has no long-haul aircraft that can range across the Atlantic. Norwegian, meanwhile, has been steadily adding to its long-distance routes.
The A4E group was launched last month and claims to account for more than half of Europe's passenger journeys.
It was also announced on Thursday that Finnair would join the alliance.
“Airlines for Europe is open for business and ready to represent the interests of all European airlines. We will grow our member base over the next months, uniting more European airlines to take forward changes that will increase our competitiveness and result in lower fares and more choice for passengers," A4E managing director Thomas Reynaert, A4E's Managing Director.
Just last week, Norwegian poked fun at Ryanair by getting involved in a minor political scandal in Denmark. Danish PM Lars Løkke Rasmussen flew to Malaga on Ryanair despite the airline's bitter battles with Danish unions and its lack of a collective bargaining agreement in the country. Rasmussen's flight angered his political opponents but provided an opportunity for Norwegian to capitalize on the scandal with a cheeky ad aimed directly at the PM.
“You are always welcome on board with us, Lars. We have both a collective bargaining agreement and free wifi!” Norwegian's Danish team posted on Facebook: