The additional metal will bring the airline’s Luton fleet to six while new routes to Alicante, Athens, Barcelona, Bologna, Cork and Malaga will mean 21 are now available from the airport.
It is expected that as many as 2.2 million passengers will now access the flights each year.
Luton Airport chief executive Nick Barton said: "Ryanair has been a big part of our success since it first started flying from LLA in 1986, and the decision to expand its presence here is a testament to our transformation into a world class international airport.
"We are currently carrying out the single biggest investment in our 80-year history to meet continued demand from passengers and give them the best travel experience possible.
"Our continued work with airline partners means that passengers now have more choice of destinations than ever before. We look forward to continuing to work with Ryanair as we grow and transform."