The prince, 32, second in line to the British throne and also known as the Duke of Cambridge, will join the East Anglia Air Ambulance, a non-governmental charity group involved in transporting sick and injured to southeastern England hospitals.
His work will begin in the spring of 2015.
"The Duke sees this as a true form of public service, helping people in their most difficult times. He regards his work with the RAF search and rescue force as having been an exceptional privilege and the Duke wanted to make his own contribution to the outstanding work of the air ambulance service," a Kensington Palace spokesman said.
Patrick Peal, the charity's chief executive, added, "We're delighted His Highness has decided to fly with us. We are confident this will help raise the profile of the charity and other air ambulance charities in the region and across the UK."
The prince's salary, which was not revealed, will be donated back to the charity, the Kensington Palace spokesman said.