Ackland, Mary Kathleen Macrory- [pseud. Valentine Ackland] (1906–1969), poet, was born on 20 May 1906 at 54 Brook Street, Mayfair, London, the younger daughter of Robert Craig Ackland (1865–1923), a West End dental surgeon, and his wife, Ruth Kathleen, née Macrory (1876/7–1961). She attended Queen's College in Harley Street and a finishing school in Paris, and came out as a débutante in 1923, the year that her father died from cancer. Her privileged upbringing and genteel education (of whose limitations she was painfully aware) prepared her for no career other than marriage, and Ackland's youth was an unhappy one, marked by sexual and religious confusion, melancholia, and alcohol addiction, all recorded with forensic self-absorption in her confessional memoir, For Sylvia: an Honest Account, published posthumously in 1985. After converting from the Anglican faith to Roman Catholicism, on 9 July 1925 she made a hasty and brief marriage to (Allan) Richard Turpin, (1903–1979), a stamp dealer and later a minor novelist. Within months she had left him (they were divorced on grounds of nullity in 1927) and had gone to live in East Chaldon, Dorset, where she became friends with the writer T. F. Powys and his family. Here she widened her circle of artistic acquaintance—which already included Augustus John and Eric Gill—to include the sculptors Stephen Tomlin and Betty Muntz. At almost 6 feet tall, with close-cropped hair, Ackland's striking physical appearance made her an attractive model to Gill and others; at the same period her adoption of Valentine as her name and pseudonym and almost exclusive conversion to masculine clothing emphasized the lesbian side of her (then) bisexual nature.

When in 1930 Ackland fell in love with the well-known novelist and poet Sylvia Townsend Warner (1893–1978), the two women set up home together in Chaldon, later living briefly in Norfolk and then back in Dorset (in Maiden Newton from 1937) for the rest of their thirty-eight-year 'marriage'. The relationship has been thoroughly documented, in Warner's Diaries (1994), Letters (1982), and the lovers' voluminous correspondence, published as I'll Stand By You (1998), which bears witness to the essential contentment of their domestic life, despite Ackland's infidelities and chronic melancholia. Much of the latter was connected with the failure, in worldly terms, of her poetry. Very little of her work was published during her lifetime other than in periodicals (including Life and Letters Today, the London Mercury, the New Statesman, Left Review, and Our Time). Early in their relationship Warner had promoted Ackland's work vigorously; the only substantial result was a joint collection, Whether a Dove or Seagull, published in 1934, which did little to launch Valentine's career though it constituted an interesting experiment in presentation, along the lines of Wordsworth's and Coleridge's jointly published Lyrical Ballads. In the melding together of the two writers' work (the poems were unattributed in the text), Warner and Ackland made a gesture against 'the frame of mind which judges a poem by looking to see who wrote it' (S. T. Warner and V. Ackland, Note to the reader, Whether a Dove or Seagull, 1934). At the same time anonymity afforded them considerable licence, and the collection is remarkable for its love poems, many of which were so sexually explicit as to pass contemporary reviewers without comment.

Ackland's growing interest in social issues and left-wing politics led her to join the Communist Party in 1935. She became a regular contributor to Edgell Rickword's Left Review, The Countryman, and the Daily Worker and in 1936 published a study of rural poverty based on her polemical journalism entitled Country Conditions. During the Spanish Civil War in 1936 she and Warner worked with the Red Cross in Barcelona and in the following year they were both delegates at the International Writers' Conference in Madrid. During the Second World War she worked as a civil defence clerk and as a doctor's dispenser. By 1953 Ackland had become disillusioned with the Communist Party and resigned. Three years later she rejoined the Catholic church (having lapsed quickly the first time) and remained in that faith until the late 1960s, when she became a Quaker.

Ackland's meditative lyric voice is most at home describing the natural world (which she does in an exaltedly scientific spirit) and has much more in common with the past writers she admired, particularly John Clare, William Cowper, Thomas Traherne, and George Crabbe, than with her contemporaries. An intuition that she was in many ways out of step with her time contributed to her ambivalence about appearing in print. Her habit of revising poems was symptomatic of a feeling that her work was always, as it were, ‘in progress’; significantly her most frequent theme is transience and the equivocal nature of ‘the moment’. The poet Wendy Mulford has characterized Ackland's poetry as 'wrestling with the paradox of feeling' (Mulford, 208), a struggle which is visible in both content and form. Written mostly in free verse, all Ackland's work contains strong undercurrents of the traditional forms from which she is deviating.

At her death in 1969, Ackland had only one publication to her name apart from Whether a Dove or Seagull, a privately printed booklet Twenty-Eight Poems (1957). Later Poems appeared in 1970, Further Poems in 1978, and a substantial selection entitled The Nature of the Moment in 1973. The attention her poetry has attracted posthumously seems to derive some of its energy from the neglect she suffered during her lifetime; Ackland's obscure (and personally disappointing) career is regarded by some critics as constituting a reproach to an earlier generation of canon-mongers (see Jane Dowson's comments on Valentine Ackland in Women's Poetry of the 1930s: a Critical Anthology, 1996). Though none of her books is currently in print, selections from Ackland's work (generally the more polemical parts of it) are included in many recent anthologies of left-wing, lesbian, and thirties' poetry. The increasing interest in Ackland both as a writer and as a minor lesbian icon is reflected in her inclusion in the Writer's Gallery at Dorset County Museum, which opened in 1997.

Valentine Ackland died from breast cancer on 9 November 1969 at her home, Lower Frome Vauchurch, Maiden Newton, and was buried at St Nicholas's Church, East Chaldon, on 22 November.