The airline and tour operator received the title for "continuing to go from strength to strength" and giving holidaymakers a "great product and service".
They also received praise for their customer service, quality, and value for money at the awards ceremony in Euston Square, London.
Nominees for the award included Audley Travel, The Landmark Trust, Ramblers Walking Holidays and Zest Car Rental.
Steve Heapy, chief executive of Jet2.com and Jet2holidays, said: "We are extremely proud to be recognised as the Which? Travel Brand of the Year once again, and it shows that Jet2.com and Jet2holidays customers continue to be in the best hands when they travel with us.
"As we gear up for our biggest ever summer programme, we will continue to place our VIP customer service at the heart of everything we do so that we carry on delivering the industry-leading levels of customer service that our customers expect."
