Travers began publishing her poems while still a teenager and wrote for The Bulletin and Triad while also gaining a reputation as an actress. She toured Australia and New Zealand with a Shakespearean touring company before leaving for England in 1924. There she dedicated herself to writing under the pen name P.L. Travers (the initials were used to disguise a woman's name). Travers also greatly admired and emulated J.M. Barrie, the writer most famous for authoring Peter Pan, which bears many structural resemblances to Travers' own greatest works, the Mary Poppins series.

In 1925 while in Ireland, Travers met the poet George William Russell (AE) who, as editor of The Irish Statesman, accepted some of her poems for publication. Through Russell, Travers met William Butler Yeats and other Irish poets who fostered her interest in and knowledge of world mythology. She had studied the Gurdjieff System under Jane Heap and in March 1936, with the help of Jessie Orage, she met the mystic Gurdjieff who would have a great effect on her, as well as on several other literary figures.

The 1934 publication of Mary Poppins was Travers' first literary success. Five sequels followed (the last in 1988), as well as a collection of other novels, poetry collections and works of non-fiction.

The Disney musical adaptation was released in 1964. Primarily based on the first novel in what was then a sequence of four books, it also lifted elements from the sequel Mary Poppins Comes Back. Although Travers was an adviser to the production, she disapproved of the dilution of the harsher aspects of Mary Poppins's character, felt ambivalent about the music and disliked the use of animation to such an extent that she ruled out any further adaptations of the later Mary Poppins novels. At the film's star-studded premiere, she reportedly approached Disney and told him that the animated sequence had to go. Disney responded by saying "Pamela, the ship has sailed." and walked away. Travers would never again agree to another Poppins/Disney adaptation, though Disney made several attempts to persuade her to change her mind. So fervent was Travers' dislike of the Walt Disney adaptation and due to the way she had been treated during the production, that well into her 90s, when she was approached by producer Cameron Mackintosh to do the stage musical, she only acquiesced upon the condition that only English born writers (and specifically no Americans) and no one from the film production were to be directly involved with the creative process of the stage musical. This specifically excluded the Sherman Brothers from writing additional songs for the production even though they were still very prolific. Original songs and other aspects from the 1964 film were allowed to be incorporated into the production however. These points were stipulated in her last will and testament.

Although she never married, at the age of 40 Travers adopted a baby boy from Ireland named Camillus, separating him from his twin brother (she refused to take both children; the boys reunited years later).

Travers was made an Officer of the Order of the British Empire in 1977. She died in London in 1996.