Harry, 18, will apply to Sandhurst military academy before taking a year off from studying. If he is accepted, he would expect to join the army late next year, Prince Charles' office at the palace said.
Like his elder brother, Prince William, Harry was expected to spend his year off working and traveling.
At Eton, Harry took part in the school's Combined Cadet Corps and was runner-up for the top accolade of Sword of Honor.
His father, Prince Charles, and grandfather Prince Philip served in the Royal Navy, and his uncle Prince Andrew was a navy helicopter pilot who served in the Falklands war.