It happened on a New Year's Day flight from Alicante to Newcastle, the airline said.
The passenger was given medical assistance on board and paramedics were requested to meet the plane when it landed, but the person died.
In a statement, the airline said: "easyJet can confirm that a passenger was taken ill on board flight EZY6418 from Alicante to Newcastle on 1 January.
"Medical assistance was provided to the passenger on board and the crew requested paramedics to attend upon landing to provide further medical assistance, however the passenger sadly passed away.
"Our thoughts are with the family and friends of the passenger and we are offering support and assistance at this difficult time.
"The safety and wellbeing of our passengers and crew is our highest priority."