After less than seven weeks of gruelling training, the prince marched in perfect step and raised his hat in three cheers to his grandmother, the queen, at the elite college's colors parade.
But the queen, who had been due to preside over the event, was absent after falling ill with a heavy cold.
General Sir Michael Walker, chief of defense staff, stood in for the monarch at the parade, the first of its type at Sandhurst for more than 30 years.
The Prince stood among 755 fellow cadets in sweltering heat during the hour-long ceremony at the military academy in Surrey.
Harry showed off his immaculately pressed uniform as he stood in line, second from the end in the second row from the back as the new colors were presented.
General Walker stopped and had a few words with the prince, who stood straight-backed, staring forward and nodded almost imperceptibly displaying his Golden Jubilee medal as the general inspected the cadets.
Tuesday's parade was the first separate presentation of new flags to the academy since 1974.
In 1991, new colors were handed over at the same time as the regular sovereign's parade.
Around 3,500 guests sat in stadium-style seating around the parade square in front of the imposing Old College building with dignitaries, including diplomats from 57 countries, taking their seats at the front.
The recruits stood motionless as prayers were read, including the line:
"We humbly beseech thee to bless thy servant our gracious Sovereign Lady Queen Elizabeth."
As the ceremony drew to a close, the prince, who was recently allowed to temporarily ditch his heavy black army boots because of blisters, marched in perfect step as the recruits paraded around the square.