Angela Margaret Thirkell (/ˈθɜːrkəl/; née Mackail, 30 January 1890 – 29 January 1961) was an English and Australian novelist. She also published one novel, Trooper to Southern Cross, under the pseudonym Leslie Parker.

Angela Margaret Mackail was the elder daughter of John William Mackail (1859–1945), a Scottish classical scholar and civil servant from the Isle of Bute who was the Oxford Professor of Poetry from 1906 to 1911. Her mother, Margaret Burne-Jones, was the daughter of the Pre-Raphaelite painter Edward Burne-Jones, and through her, Thirkell was the first cousin once removed of Rudyard Kipling and Stanley Baldwin. Her brother, Denis Mackail (1892–1971), was also a novelist and they had a younger sister, Clare. Angela was tall, "with legs like columns, and large, masculine feet" and she ruled over her younger cousins and siblings, who called her AKB—Angela Knows Best.

Angela Mackail was educated in London at Claude Montefiore's Froebel Institute, then at St Paul's Girls' School, Hammersmith, and in Paris at a finishing school for young ladies.

Soon after her return from Paris, Angela Mackail met James Campbell McInnes (1874–1945), a professional singer, and married him in 1911. Their first son was born in January 1912 and named Graham after McInnes's former lover, Graham Peel. Their second son was the novelist Colin MacInnes. A third child, Mary, was born and died in 1917, and Angela then divorced her husband for adultery, in a blaze of publicity. In December 1918, Angela married George Lancelot Allnut Thirkell (1890–c. 1940), an engineer of her own age originally from Tasmania, and in 1920 they sailed for Australia together with her sons. Their son Lancelot George Thirkell, later Comptroller of the BBC, was born there. The Thirkells led a 'middle-middle-class life' in Melbourne, which to Angela was all deeply unfamiliar and repugnant. So, in November 1929, Angela left her husband without warning, returning to England with Lancelot George, on the pretext of a holiday, but in fact quitting Australia for good.

Lacking money, she begged the fare to London from her godfather, J. M. Barrie, and used the sum intended for her return ticket for two single passages, for herself and her youngest son. She claimed that her parents were aging, and needed her, but she certainly also preferred the more comfortable life available with them in London. Her second son, Colin, followed her to England soon after, but Graham stayed in Melbourne.

Thereafter, her "attitude to any man whom she attracted was summed up in the remark: 'It's very peaceful with no husbands,'" which was quoted by the Observer newspaper in its column 'Sayings of the Week'.

Thirkell began writing early in her life in Australia, chiefly through the need for money. She published an article in the Cornhill Magazine in 1921, the first of many articles and short stories, including work for Australian radio. On her return to England in 1929, this career continued with journalism, stories for children, and then novels. Her success as a novelist began with her second novel, High Rising (1933). She set most of her novels in Anthony Trollope's Barsetshire, his fictional English county developed in the six novels known as the Chronicles of Barsetshire. An alert reader of contemporary fiction, Thirkell also borrowed freely from little known titles like John Galsworthy's The Country House, from which, for example, she lifted the name 'Worsted' which she used for the village setting of her novel August Folly (1936). She also quoted frequently, without attribution, from novels by Charles Dickens, William Thackeray and Elizabeth Gaskell. Thirkell published a new novel every year, which she referred to in correspondence with her editor, Jamie Hamilton of Hamish Hamilton, as new wine in an old bottle. She was upset that her circle of well educated and upper-middle-class friends thought her novels "too popular" knowing they preferred, as she did, such writers as Gibbon, Austen, Dickens and Proust. She drew the epigraph to T 1951 from Proust: "Les gens du monde se représentent volontiers les livres comme une espèce de cube dont une face est enlevée, si bien que l'auteur se dépêche de 'faire entrer' dedans les personnes qu'il rencontre" ("Society people think that books are a sort of cube, one side of which the author opens the better to insert into it the people he meets.")

Her books of the 1930s in particular had a satiric exuberance, as in Pomfret Towers, which sends up village ways, aristocratic folly and middle-class aspirations. Three Houses (1931, Oxford University Press; repeatedly reprinted) is a short childhood memoir which simultaneously displays Thirkell's precociously finished style, her lifelong melancholy, and her idolisation of her grandfather, Edward Burne-Jones. Trooper to the Southern Cross (1934; republished in 1939 as What Happened on the Boat) "is concerned with the experiences of a number of English and Australian passengers aboard a troop-ship, the Rudolstadt, on their way back to Australia immediately after World War I. It is particularly interesting for its depiction of the Australian 'digger'; his anti-authoritarianism, larrikinism, and, at the same time, his loyalty to those whom he respects". Thirkell's 1936 publication August Folly was chosen the Book Society's Book of the month. This embarrassed her as it seemed to define the book as insufficiently artistic. leading her to write to her publisher that "I can only hope that the financial gain involved will counterbalance the moral degradation."