British actress and activist was a child in 1953 when Elizabeth II was crowned Queen of England - and her devotion to the long-serving monarch hasn't wavered since.
In honour of the queen's platinum jubilee (70 years on the throne), Lumley has published a new book celebrating her extraordinary life of service - A Queen for All Seasons.
When Lumley was invited to do the book, she tells Kim Hill it seemed like a wonderful opportunity to hand "a bouquet of tributes" to the 95-year-old.
"[Elizabeth II] was ten when her uncle Edward [VIII] suddenly abdicated and she was propelled from being a royal princess… to the Queen of England. She knew when she was ten she was going to be the Queen of England."
As the Queen chooses never to be interviewed, part of the impetus for the book was trying to find out what she's really like from lots of people who've met her.
People have remarked that Elizabeth II seems to have a "sixth sense" with horses, dogs and troubled people, Lumley says, and an anecdote in A Queen for All Seasons by Welsh doctor David Nott illustrates this.
The queen once invited Nott, who'd recently been a war doctor in Syria, to a small lunch party where he was seated next to her. Nott recalls that when Queen Elizabeth enquired about his time in Syria, he found himself upset and unable to speak.
"The queen noticed that at once, patted him on the hand, quickly took some biscuits out of a little box on the table and said 'let's feed the dogs', then bent down and fed the corgis which were under the table. And then talked to him about her dogs and things.
"I think she was so aware of the fact that he was overcome with emotion at the horrors he had seen. And I find it so very touching."
Lumley, now 75, says she has very much enjoyed meeting the Queen and many other members of the British royal family at functions.
"Regardless of what the press thinks of them, [the royal family are] all completely charming and friendly and non-grand … They're completely friendly and put you at ease and they're sweet and warm."
When it comes to representing a country, members of the monarchy have training on their side, she says.
"Should [positions of power] be inherited or should we vote these people in and out? Well, maybe we should. But then when you think of presidents who come and go and their failings and sometimes they jump ship and sometimes they're found out. Sometimes they're good but then they die...
"There's a constancy about someone whose been trained for the job and that' their job. They've been brought up never to jump ship. So I think monarchy - odd though it may seem - is one of the ways of representing the country."
A black-and-white film of the Queen's coronation glimpsed by a 7-year-old Joanna Lumley in her school hall in Malaysia seemed like a fairy story, she says.
"[There was] a bit of rain on the streets and these great clanking carriages with horses, crowds yelling and the streets covered with streamers and flags. And then this diminutive figure - with a crown and ladies in waiting and a great long train… I thought then, isn't she terrific?
"Of course there was intense excitement to see somebody whose face you already knew from stamps and coins and pictures and photographs in the paper."
At age 21, instead of having a wild party, Elizabeth II made a solemn speech vowing to dedicate her life to serving the Commonwealth - and she has kept that promise to an extraordinary degree, Lumley says.
"She's never done anything but do her duty and do it with grace and compassion and kindness. And what a hell of a life it is.
"We're all people underneath, we all know that. But she's fashioned her life around this sense of duty and obligation and she's done it absolutely without faltering."
Despite the grandeur that has surrounded Queen Elizabeth, Lumley thinks the queen herself is actually "quite down to earth and countrified".
An incident from the queen's 1953-1954 visit to New Zealand, which features in A Queen for All Seasons, seems to confirm this.
When a group of Invercargill royalists began chanting the night away outside her hotel room, Elizabeth II was forced to sleep on an iron bed in the staff quarters, Lumley says.
"I love the idea of her sleeping in her little iron bed. I wouldn't think she would mind a bit… I'd think she slept like a lamb in that little iron bed with the ironing board next door to her."
Lumley likes to think she's a good traveller herself, having experienced all kinds of accommodation while filming her travel shows, which include Joanna Lumley's Silk Road Adventure.
"I don't mind where I sleep. I don't mind washing out of a bucket. I don't mind what other people might see as hardships."
Lumley is currently filming the travel show Secret Cities which will be released next year and her new film Falling for Figaro opens in New Zealand cinemas on 18th November.
Ahead of that, Lumley's ITV documentary The Human Swan - about the adventurer and conservationist Sacha Dench - will screen at the UN Climate Change Conference COP26.
With her TV work and activism - she has campaigned for the rights of Gurkhas and against animal testing and the importation of foie gras - Lumley concedes that now, in her mid-70s, she's probably busier than ever.
"The thing is if you want something done now ask a busy person. That's a Chinese proverb. And I'm a busy person.
"If you focus and work hard and make a list of to-do things and then do them, you can get through much more than you ever thought possible."