But disappointed by the Disney film, the Australian-born author wasn't keen to see it adapted for stage.
It wasn't until Mackintosh met Travers in 1993 (she died in 1996 at the age of 96) that she entrusted him with the stage rights - on the condition that only English-born writers could be involved, and excluded anyone who'd been part of the film adaptation, including the Sherman brothers, who wrote the songs.
"From what I hear she was much happier with Mackintosh's plans for the stage show than she was with the film," explains Matt Lee, who plays Bert.
"I think the books tell a darker story, and I think that's the kind of element that's been brought to the stage show. It became quite a squeaky clean Disney film, which is so iconic and so successful, but I think Pamela had a different idea of where she wanted the story to go."
Indeed on this second to last night in Perth's Burswood Theatre the production moves seamlessly between the huge iconic set-pieces like Step in Time (which has the chimney-sweeps tap dancing their way across London, and Bert even dances upside down on the theatre roof), and back to more intimate moments with the family.
It ranges from comedy to melancholy, and isn't afraid to bare the heaviness of poverty.
The beautifully spare ballad Feed the Birds, sung by the homeless bird woman (played by New Zealander Delia Hannah), is goosebump-inducing, and the ever catchy Supercalifragilisticexpealidocious is a triumph of choreography, a colourful masterpiece in which everyone on stage spells out the word in a series of hand signals at extreme pace.
The set is a key part of the magic but it's not reliant on any complex technology or animated screens, instead set designer Bob Crowley was inspired by the original book illustrations by Mary Shepard, and wanted to capture that hand-drawn effect to invoke childhood nostalgia.
They're beautifully old-fashioned and intricate, and though Jolly Holiday has to lose the cartoon penguins and race horses of the film, they recreate the wizardry with an eye-popping change from black and white to colour - and a pair of comic sheep.
Though set in Edwardian times, the story has contemporary resonances.
Despite their upper-class appearances, the Banks family of 17 Cherry Tree Lane are unhappy. Father George, a banker, works too hard and has no time for his family. His children Jane and Michael feel neglected, and his wife Winifred is stuck in the middle.
Simon Burke - who plays the gruff, strict George (who thinks a family home should be run with precision) - has found there's a lot for 21st century fathers to relate to in the Edwardian tale.
"The fascinating thing about playing George is that so many dads who've been dragged along kicking and screaming to a musical, have really related to this guy who's working like crazy, and he's just unavailable to his family - emotionally, and even physically, because he's just not there.
"His kids aren't really on his radar, and then suddenly, at the end, he realises that they're going to grow up soon, so he's desperate to put his family back together.
"So they've locked in some modern themes and considerations for the audience, but kept the characters very period."
Mackintosh who launched the show in 2004, aimed to keep it truthful and emotional without being saccharine, and the show manages to avoid any preachiness by weaving the life lessons which Mary teaches into magical adventures, and a strong sense of oddball whimsy.
There's also more dry wit and sly adult humour than might be expected from a Disney musical, and that could possibly be credited in part to Julian Fellowes (the creator of Downton Abbey), who adapted the story for the stage.
Both Burke and Pippa Grandison, who plays Winifred Banks, admit the key to connecting with the younger audience members is the young performers who play Jane and Michael - there are usually four pairs who rotate for each production.
"The children in the show really make it work because then the kids in the audience see it through their eyes and it holds them," says Grandison.
"I'm constantly amazed at how many kids will stay focused through the whole show - occasionally they yell out whenever they like, and you think, 'ooh we've got a live one', but mostly they're very absorbed."
The quality of the performances of these young stars is exceptional, and is important to the success of the whole show, explains Burke explains
"They have more time than anyone on stage, more time than Mary Poppins, so they're huge roles, they're the stars. And luckily they're hilarious."
There is palpable enthusiasm from the whole cast, who are seemingly delighted to be involved in the production, despite performing the show eight times a week for months on end, with some of them having performed 800 shows over the two years it has been running in Australia.
Lee, who's been dancing since he was 5, and is known to Aussie TV audiences as a judge on So You Think You Can Dance and The Voice, was thrilled to be cast as Bert, the role played by Dick Van Dyke - with an infamously bad Cockney accent - in the movie.
"They're quite rare for men, these 'triple threat roles' [singing, dancing and acting], and it was amazing to be cast in such an iconic role in such an iconic show. There are generations who've grown up reading the books or watching the film, the fact that they've finally got in on stage.
"I think the adults come expecting to see a kids' show, and they're the ones who are actually quite affected when they leave.
"People say things like 'Oh I felt like a kid again', and Mary often comments that when she flies out over the audience at the end, and can see everyone below her, it's often the men that are crying."
A walk down Cherry Tree Lane
Mary Poppins was originally a series of books by Australian-born, eventually England-based author P.L. (Pamela) Travers, who died aged 96 in 1996. The first was published in 1934, followed by seven sequels, with the last one published in 1988.
Walt Disney first approached Travers for the film rights as early as 1938, but she was reluctant as she didn't believe a film version would do justice to her creation and did not want an animated cartoon based on it. Disney finally succeeded in 1961, though Travers demanded script approval rights.
It ended up being Disney's first non-animated film (albeit one with a small cartoon scene) and was released in 1964, starring Julie Andrews in her movie acting debut, along with Dick Van Dyke.
Andrews won the Academy Award for Best Actress, and the film also won Oscars for Best Film Editing, Original Music Score, Best Song and Best Visual Effects, and received a total of 13 nominations.
It was also the No 1 film at the box office in 1965, and has grossed more than US$102 million in the United States.
The much-loved songs, including A Spoonful of Sugar, Chim Chim Cher-ee, Jolly Holiday, Let's Go Fly A Kite, and of course Supercalifragilisticexpealidocious were written by the Sherman brothers, Richard and Robert.
Eight new songs have been written for the theatre show to expand characters, and introduce a few darker elements than were present in the film.
Lowdown
What: Mary Poppins the Disney musical
Where and when: Civic Theatre in Auckland from October 18 to December 30
