The announcement, which Sky News reported at the weekend was imminent, was made just over two months after the commercial broadcaster admitted Adam Crozier was to step down as chief executive.
Dame Carolyn's move to ITV to become its first female boss marks a return to the media industry for her - having previously run the Guardian Media Group - after seven years in the airline's corporate cockpit.
"Having first built a solid operational performance, she redefined the customer experience not just at easyJet but across short-haul Europe and has seen both the number and loyalty of easyJet's passengers grow as a result."
Its shares were 0.8% lower in early trading though later turned positive and closed 1.4% higher while those of ITV were up 1.3% by the end of the session.
The airline said it had begun the search for her successor, who will take over at a crucial time for the industry ahead of Brexit.
It announced on Friday it was creating a new, Austrian-based airline to help it navigate the potential turbulence of regulation after the UK's departure from the EU.
ITV said Dame Carolyn would get down to work in her new role from 8 January.
Its chairman, Peter Bazalgette, said: "In a very impressive field of high calibre candidates, Carolyn stood out for her track record in media, experience of an international operation, clear strategic acumen and strong record of delivering value to shareholders.
"I'm delighted we'll be working together at ITV."
She added: "I'm really pleased to be joining ITV. It is a fantastic company in a dynamic and stimulating sector.
"I am looking forward to getting to know all of the people at ITV and helping it make the most of the amazing opportunities that it has in the future."
ITV said her pay arrangements would be "broadly" similar to those of Mr Crozier with an annual salary of £900,000 and a pension allowance of 15% of salary.
It said: "She will also be able to participate in the company's existing annual bonus plan up to a maximum of 180% of salary, and the long-term incentive plan up to 265% of salary."
She will also, ITV added, receive awards to compensate for remuneration arrangements forfeited on leaving easyJet.