In the poetically rich quarter century between 1950 and 1980, Isabella Gardner earned a wide-ranging and considerable reputation in poetry, her chosen vocation. Born on September 7, 1915, she was raised in Boston, one of six children of George Peabody and Rose Grosvenor Gardner. She was a cousin of poet Robert Lowell and was often confused with the other Isabella Stewart Gardner, the Boston art patron and collector, who was her great-great-aunt and godmother. At one time in her life she even lived in her godmother's house, and, according to many, with her red hair and snub nose, she also looked like her.

Gardner's education included the Foxcroft School in Middleburg, Virginia, from 1931 to 1933, the Leighton Rollins School of Acting in East Hampton, New York, and in 1937, the Embassy School of Acting in London, England. For a few years she pursued an acting career, specializing in character roles "where her shy stutter would be less liable to obtrude." After marriage and the birth of her children, she resumed the writing of poetry, which she had begun in her early teens and had given up because she believed herself to be "too facile" at the craft. Once renewed, however, her position as a poet-contemporary of such writers as Howard Shapiro, John Logan, Richard Eberhardt, John Frederick Nims, William Carlos Williams, Marianne Moore, and Elizabeth Bishop was secured.

Although her output was comparatively slim (about 100 published poems), Gardner’s work appeared in such prestigious literary journals and magazines as Poetry, Partisan Review, Paris Review, the New Yorker, Nation, and Atlantic Monthly. There were five books of poetry: Birthdays from the Ocean (1955), Un Altra Infanzia (in Italy, 1959), The Looking Glass (1961), West of Childhood: Poems 1950-1965, and posthumously, The Collected Poems (1985). Her work was anthologized in, among others, A Pocket Book of Modern Verse (1955), Imagination's Other Place (1955), Erotic Poetry (1963), Eight Lines and Under (1967), and Honey and the Gall (1967). Sound and rhythm are crucial elements in Gardner's poetry. She makes extensive use of rhyme, including internal rhyme and "near-rhyme," and there is an exuberant musicality in her poems, even while many of them explore death-related themes. After the breakup of her marriage to Allen Tate, Gardner withdrew to a somewhat reclusive existence in the Chelsea Hotel in New York City and a self-imposed poetic silence of 15 years. Her later poems, in a slight nod to changing poetic fashions and trends, went to longer lines and even an abandonment of the brilliant end rhyme that had been so characteristic of her.

From 1951 to 1956, Gardner was associate editor of Poetry, under the editorship of Karl Shapiro. There she became known for her caring concern for the success of younger poets she worked with, even providing monetary help in some cases. Birthdays from the Ocean and The Looking Glass were nominated for the National Book Award, That Was Then was nominated for the 1980 American Book Award, and in 1981 Gardner was selected as the first recipient of the New York State Walt Whitman Citation of Merit for Poetry. Gardner died July 7, 1981. She had been married four times: Harold van Kirk, 1938 (marriage ended); Maurice Seymour, 1943 (divorced 1947); Robert H. McCormick Jr., 1947 (divorced 1957); and Allen Tate, 1959 (divorced 1966). She also had two children, Rose Van Kirk and Daniel Seymour.