The announcement ends speculation the prince would end his military career next year to concentrate on being a full-time royal, The Daily Telegraph reported Monday.
Instead, he will go through 18 months of training, then serve on the air search-and-rescue team for a minimum of 30 months, the Telegraph said, adding the prince would be at least 31 years old before returning to civilian life.
"It has been a real privilege to have spent the past year understanding and experiencing all aspects of the British armed forces," Prince William said in a statement. "I now want to build on the experience and training I have received to serve operationally -- especially because, for good reasons, I was not able to deploy to Afghanistan this year with D Squadron of the Household Cavalry Regiment."
The prince said his time with the Royal Air Force made him realize how much he enjoys flying. Joining the search-and-rescue unit is a "perfect opportunity" for him to serve in the forces and contribute to a "vital part" of the country's emergency services, he said.