The royal sat next to Vice President Joe Biden at the wheelchair rugby finals, where USA beat Denmark.
The politician gave a speech at the event, praising Harry who founded the Invictus Games, while also joking that his wife Jill "spent too much time" with Harry at the 2014 games.
Mr Biden went on to praise the wounded servicemen and women for being the "spine and backbone" of the country. "Thanks for being who you are," he said.
The vice president also paid tribute to his son Beau, who died in 2015 following a battle with brain cancer.
"We're a military family," he said. "Our son Beau was a major. He used to have a saying and he lived it, he'd say "never complain and never explain". And he lived it."