For most of her working life, teaching English and French, and making a living took priority and writing was done only in her spare time. Already established Australian writer Thea Astley, who taught with Witting at Cheltenham Girls High School, was impressed by one of her stories, Goodbye, Ady, Goodbye, Joe, and encouraged her to submit it for publication. It was published in The New Yorker in April 1965. Indeed, the poet Kenneth Slessor told Thea Astley to "tell that women I'll publish any word she writes".
In 1974, using the pseudonym Chris Willoughby, she wrote a lampoon for Tabloid Story as the result of her anger a "the sexism of the Frank Moorhouse/Michael Wilding tabloid Story tales of sex with an unconscious drugged girl at a party". Her story outraged parents, politicians and teachers; the Minister for Education accused her of corrupting children and stated in Parliament that "Amy Witting is a scribbler on lavatory walls". However, this did not harm her career, and three years later she was mistress of modern languages at North Sydney Girls' High School.
However, her success came late in life when, in retirement, she could spend more time on her writing. Her first novel, The Visit was published by well-known Australian editor Beatrice Davis. However she rejected I for Isobel on the grounds that "No mother has ever behaved so badly" and McPhee Gribble also rejected it saying that "It's difficult to see what market you had in mind for it". However, it was published by Penguin Books and became an instant best seller. It was with the publication of this book that her talent was finally recognised.
Critic Peter Craven suggests that while her "poetry is the work of a writer who has mastery of any meaning she wishes to convey, [her] fiction took some time to reach fruition, partly because the publishing climate which would be receptive to Witting's brand of realism had to wait the advent of such writers as Helen Garner. Craven writes that "Witting was a great master of realism, a naturalist who could render a nuance in a line that might take a lesser writer a page".
Her last three works – Isobel on the Way to the Corner Shop, Faces and Voices, and After Cynthia – were written under difficulty: her sight and hearing were failing, and she was stricken with cancer.