The private audience was followed by an official reception and dinner - during which Harry gave a speech.
Harry said: “We are deeply grateful to you all for welcoming Meghan and me to Tongatapu (the main island of Tonga) and to Your Majesties for making us feel at home here.”
He also read a message from his grandmother, the Queen.
It said: “Your Majesties, it gives me great pleasure that my grandson and his wife are visiting the Kingdom of Tonga.
“Our two families have enjoyed a deep and warm friendship over many years, and I hope that our close relationship continues with the next generation.
“To this day, I remember with fondness Queen Salote’s attendance at my own Coronation, while Prince Philip and I have cherished memories from our three wonderful visits to your country in 1953, 1970 and 1977.
“In the months and years ahead, I wish Your Majesties and the people of Tonga every good fortune and happiness.”
The duke signed off his speech with “malo ‘aupito”, Tongan for “thank you very much”.