The Brexit Party leader also described the Queen's late mother as "a slightly overweight, chain-smoking gin drinker" in a series of derisive comments about members of the Royal Family, it has emerged.
Mr Farage is said to have made the remarks during a gala dinner - at Sydney's Conservative Political Action Conference - and focused his criticism on the climate change views of the Duke and Duchess of Sussex and Prince Charles.
The Guardian has heard a partial recording of Saturday night's event, at which media were claimed to have been barred from attending.
"When it comes to her [the Queen's] son, when it comes to Charlie Boy and climate change, oh dear, oh dear, oh dear," Mr Farage is reported to have said in relation to Prince Charles and his succession to the throne.
"Her mother, Her Royal Highness the Queen's mother was a slightly overweight, chain-smoking gin drinker who lived to 101 years old.
"All I can say is Charlie Boy is now in his 70s… may the Queen live a very, very long time."
Mr Farage was also said to have commented on the Duke and Duchess of Sussex's recent revelation that they want a maximum of two children due to their concerns about the climate.
"Well, if I want the Queen to live a long time to stop Charlie Boy becoming king, I want Charlie Boy to live even longer and William to live forever to stop Harry becoming king," Mr Farage is reported to have added.
"Terrifying! Here was Harry, here he was this young, brave, boisterous, all male, getting into trouble, turning up at stag parties inappropriately dressed, drinking too much and causing all sorts of mayhem.
"And then, a brave British officer who did his bit in Afghanistan. He was the most popular royal of a younger generation that we've seen for 100 years.
"And then he met Meghan Markle, and it's fallen off a cliff.
"We've been told in the last week that Meghan and Harry will only have two children.
"And we're all completely ignoring, the real problem the Earth faces, and that is the fact the population of the globe is exploding but no one dares talk about it.
"No one dares deal with it, and whether Prince Harry has two kids is irrelevant given there are now 2.6 billion Chinese and Indians on this Earth."
However, Mr Farage was said to have been more complimentary about the Queen, describing her as "an amazing, awe-inspiring woman, we're bloody lucky to have her".
In their own account of the event, the Sydney Morning Herald reported that Mr Farage told the audience that Prince Harry had become the "prince of wokeness" since meeting his wife.
Mr Farage repeated some of his comments about the Royal Family during an appearance on Sky News Australia's Outsiders programme on Sunday morning.
Remembering a previous encounter with Prince Charles, Mr Farage said: "He came to the European Parliament 10 years ago to tell us that within seven years the polar ice cap would disappear completely.
"At the end of his speech I refused to stand.
"All I can say about the Queen and his succession is this: The Queen Mother was a chain-smoking gin-drinker who did not look after herself at all and lived to 101.
"The Queen is 93 and looks fit. May she reign for a very long time."
Buckingham Palace said it would not comment on the remarks.