Barton only stepped down from his role on 1 December after almost nine years.
Johan Lundgren, easyJet chief executive, said: "I am truly shocked and extremely saddened to hear of John’s passing.
“I was very fortunate to have worked closely with him over the years and benefited greatly from his wise counsel. He was a man of huge integrity who was very much liked and respected by everyone across the airline.
“On behalf of all of his former colleagues at easyJet, we send our heartfelt sympathies to John’s family at this time. He will be greatly missed."
Stephen Hester, Barton’s successor, added: "John was a distinguished chair and made an outstanding contribution to the company during his tenure. He was also a wonderful human being. On behalf of the board, I would like to extend our deepest sympathies to John’s family at this difficult time."
