The first Jet2.com flights took off from Stansted to Alicante and Faro, while the inaugural flights from Birmingham went to Malaga.
At Stansted the first holidaymakers to depart were given personalised gifts, and those first in line to check-in won free holidays.
Actor Will Mellor also joined in the celebrations.
The group has already added more routes and aircraft to its programme since going on sale in September 2016, and will fly to 27 leisure destinations from Stansted, using seven new Boeing 737-800 next generation aircraft.
Stansted will be Jet2.com and Jet2holidays’ fourth biggest UK base.
At Birmingham airport, the company will fly to 23 destinations, with flights operating on four of Jet2.com and Jet2holidays’ new Boeing 737-800s.
Jet2holidays also hosted one of its mobile travel agency stores at the Bull Ring in Birmingham, cobranded with Midcounties Co-operative Travel, where free flights were given away.
