Walt Disney's daughters fell in love with the Mary Poppins books and made him promise to turn them into a film; he first tried to buy the rights from P. L. Travers as early as 1938, but she refused for over 20 years, fearing a film would not do the books justice.

Disney finally secured the rights in 1961, but Travers demanded and obtained script-approval rights, and remained an on-set consultant despite disapproving of many changes.

Travers hated the use of animation so much that she ruled out any further film adaptations of the later Mary Poppins novels, and she wanted the soundtrack to feature existing Edwardian-era standards rather than new songs, though Disney overruled her thanks to his final-cut privilege.

Many actresses were considered for the title role, including Julie Harris, Angela Lansbury, Bette Davis, Judy Garland, Barbara Eden, Elizabeth Taylor, Jayne Mansfield, Natalie Wood, and Elizabeth Montgomery, before Julie Andrews was cast in her feature film debut.

Julie Andrews was cast as Mary Poppins soon after being passed over for the role of Eliza Doolittle in My Fair Lady (a part she had originated on Broadway) in favor of Audrey Hepburn; Andrews went on to win the Best Actress Oscar for Mary Poppins, a category for which Hepburn was not nominated.

When Disney approached Julie Andrews about the role, she was three months pregnant, so Disney offered to postpone filming until after she gave birth so she could still take the part.

Dick Van Dyke lobbied to also play the elderly Mr. Dawes Sr. in addition to Bert; Disney initially felt he was too young, but Van Dyke won him over with a screen test. In the end credits he is first credited under the anagram 'Navckid Keyd' before the letters unscramble to reveal his real name.

Sean Connery, Cary Grant, and Andy Griffith were among the actors considered for the role of Bert before it went to Dick Van Dyke, whom Disney cast after seeing him on The Dick Van Dyke Show.

Van Dyke struggled with Bert's Cockney accent despite coaching from English actor J. Pat O'Malley; it was later ranked the second-worst film accent in a 2003 Empire magazine poll, and in 2017 Van Dyke jokingly apologized to BAFTA for it.

Marni Nixon, famous for dubbing singing voices for actresses like Audrey Hepburn in My Fair Lady, voiced the three singing Cockney geese in the 'Jolly Holiday' sequence.

Robert Sherman, one of the film's songwriters, provided the spoken line 'Feed the birds, tuppence a bag' for actress Jane Darwell's Bird Woman character because her own voice was too soft to be heard on the soundtrack.

The film was shot entirely at the Walt Disney Studios in Burbank, California, using painted London background scenes, with filming taking place between May and September 1963 and post-production/animation taking another eleven months.

The scene where Mary Poppins and Bert interact with animated penguins used the sodium vapor process instead of bluescreen: actors were filmed against a white screen lit with yellow sodium vapor lights, and a special prism-fitted camera created a highly accurate matte, even letting background light show through Mary Poppins's veil. This technique won the film the Academy Award for Best Visual Effects.

According to dancer Peter Menefee, the choreography for the rooftop chimney sweep dance was only set once the performers arrived on set, and the very first scene filmed was actually the final dance sequence, made harder because they had rehearsed on a plywood floor but had to perform on a real cobblestone street.

Walt Disney personally attended rehearsals for the rooftop dance scenes every day.

P. L. Travers was not initially invited to the film's premiere but managed to obtain an invitation through a Disney executive; at the after-party she told Disney the animated sequence had to be removed, to which he replied, 'Pamela, the ship has sailed,' and walked away.

Mary Poppins received a record 13 Academy Award nominations for a Disney-produced film, winning five, and was the only Disney film to receive a Best Picture nomination during Walt Disney's lifetime.

Walt Disney used the film's huge profits to purchase land in central Florida and finance the construction of Walt Disney World; the MAPO (MAry POppins) safety system on Disney monorails and a similar boiler safety device on Walt Disney World Railroad locomotives are named in reference to the film.

In February 2024, the British Board of Film Classification reclassified Mary Poppins from a U to a PG rating due to Admiral Boom's use of the word 'hottentot' to refer to the dancing chimney sweeps.

P. L. Travers remained so displeased with how Disney had handled her work that when producer Cameron Mackintosh approached her about a stage musical adaptation in the 1990s, she agreed only on the condition that he use exclusively English-born writers and that no one from the film production be directly involved.