She was born in New York City in 1893. Her father, Ricardo de Acosta, was of Cuban and Spanish descent and her mother, Micaela Hernández de Alba y de Alba, was Spanish and reportedly a descendant of the Spanish Dukes of Alba. De Acosta had five siblings: Aida, Ricardo Jr., Angela, Maria, and Rita. Maria married socially prominent A. Robeson Sargent, the Harvard-educated landscape architect and son of Charles Sprague Sargent. Rita became a famous beauty best known as Rita Lydig. She was photographed by Adolf de Meyer, Edward Steichen, and Gertrude Käsebier, sculpted in alabaster by Malvina Hoffman, and painted by Giovanni Boldini and John Singer Sargent among others. Under the name Mrs Philip Lydig, Rita wrote a novel, Tragic Mansions (Boni & Liveright, 1927), a society melodrama described as "emotionally moving and appealing" by The New York Times. De Acosta attended elementary school at the Covenant of the Blessed Sacrement on West 79th Street in Manhattan where Dorothy Parker was a classmate.
De Acosta married painter Abram Poole (January 1883 Chicago, Illinois – May 24, 1961) in 1920. They divorced in 1935.
She was described in 1955 by Garbo biographer, John Bainbridge, as "a woman of courtly manners, impeccable decorative taste and great personal elegance... a woman with a passionate and intense devotion to the art of living... and endowed with a high spirit, energy, eclectic curiosity and a varied interest in the arts."
De Acosta was involved in numerous lesbian relationships with Broadway's and Hollywood's elite and she did not attempt to hide her sexuality; her uncloseted existence was very rare and daring in her generation. In 1916 she began an affair with actress Alla Nazimova and later with dancer Isadora Duncan. Shortly after marrying Abram Poole in 1920, de Acosta became involved in a five-year relationship with actress Eva Le Gallienne. De Acosta wrote two plays for Le Gallienne, Sandro Botticelli and Jehanne de Arc. After the financial failures of both plays they ended their relationship.
Over the next decade she was involved with several famous actresses and dancers including Greta Garbo, Marlene Dietrich, Ona Munson, and Russian ballerina Tamara Platonovna Karsavina. Additional unsubstantiated rumors include affairs with Pola Negri, Eleonora Duse, Katherine Cornell, and Alice B. Toklas.
It has often been said that she once stated, "I can get any woman away from any man" but there is no evidence to substantiate this claim.
An ardent liberal, de Acosta was committed to several political causes. Concerned about the Spanish Civil War, which began in 1936, for example, she supported the loyalist Republican government that opposed the fascist Franco regime. A tireless advocate for women's rights, she wrote in her memoir, "I believed...in every form of independence for women and I was...an enrolled worker for women's suffrage."
She also became a vegetarian and, out of respect for animals, refused to wear furs.
De Acosta's best-known relationship was with Greta Garbo. When Garbo's close friend, author Salka Viertel, introduced them in 1931, they quickly became involved. As their relationship developed, it became erratic and volatile with Garbo always in control. The two were very close sporadically and then apart for lengthy periods when Garbo, annoyed by Mercedes' obsessive behavior, coupled with her own neuroses, ignored her. In any case, they remained friends for thirty years during which time Garbo wrote de Acosta 181 letters, cards, and telegrams. About their friendship, Cecil Beaton, who was close to both women, recorded in his 1958 memoir, "Mercedes is [Garbo's] very best friend and for 30 years has stood by her, willing to devote her life to her".
Although it has been argued that an intimate relationship between them cannot be proved, de Acosta states they were lovers. Contrary to legend, she did not do so in her memoir. In 1959, when she was destitute, de Acosta sold her papers to the Rosenbach Museum & Library in Philadelphia and claims to have reluctantly included romantic letters from Garbo. "I would not have had the heart or courage to have burned these letters", she wrote William McCarthy, curator of the museum. "I mean, of course, Eva [sic], Greta's and Marlene's who were lovers.... I only hope...they will be respected and protected from the eyes of vulgar people". All of Garbo's and de Acosta's recent biographers, moreover, discuss their involvement. Per de Acosta's request, Garbo's letters were made available to the public in 2000, ten years after her death, and none were explicitly romantic. It should be noted that Garbo's family, which controls her estate, has permitted only 87 letters to be made public.
In the early 1930s de Acosta developed an interest in Hinduism and was encouraged to seek out Indian mystic Meher Baba when he arrived in Hollywood. For several years she was captivated by his philosophy and methods and he often gave her advice about ways to address her problems. Later, she studied the philosophy of Hindu sage Ramana Maharishi who introduced her to yoga, meditation, and other spiritual practices she hoped would help ease her suffering. In 1938, she met Hindu dancer Ram Gopal in Hollywood. They immediately established a rapport and became close lifelong friends. Later that year they traveled to India to meet Maharishi.
When asked about religion, de Acosta once said that although she had grown up Catholic, she would be, if she had to be anything, a Buddhist.
In 1960, when de Acosta was seriously ill with a brain tumor and in need of money, she published her memoir, Here Lies the Heart. The book was well-received by the critics and many close friends praised the book. But its implied homosexuality resulted in the severance of several friendships with women who felt she had betrayed their sexuality. Garbo also ended their friendship at this time. Eva Le Gallienne in particular was furious, denouncing de Acosta as a liar and stating that she invented the stories for fame. This characterization is inaccurate since many of her affairs and relationships with women, including that with Le Gallienne, are confirmed in personal correspondence. An exception to this was Marlene Dietrich, who continued to correspond with her and loved the book. According to critic Patricia White, "If she craved being seen, MdA was more careful about what she said than she is given credit for. She wrote a name-dropping memoir, but for something attacked for exaggeration, it barely alludes to homosexuality". In any case, she gained a reputation that was not appreciated by everyone. But as Alice B. Toklas, lover of Gertrude Stein and de Acosta's long-term friend, wrote to a disapproving critic, "Say what you will about Mercedes, she's had the most important women of the twentieth century".
De Acosta died at age 75 in poverty. She is buried at Trinity Cemetery in Washington Heights, New York City.
De Acosta has usually been described disparagingly, dismissed as a "notorious lesbian" who was a dishonest nuisance to her lovers and who consistently "stalked" Garbo. Garbo's biographers, for example, assess their relationship from Garbo's perspective in which Garbo is fundamentally blameless in their difficult relationship, a perpetual victim of de Acosta's alleged irksome behavior. But Robert A. Schanke, de Acosta's recent biographer, attempts, on the basis of extensive research, to provide an accurate picture of her. She was, Schanke acknowledges, flawed and imperfect, a complex woman who impaired several of her relationships and failed to achieve her professional and romantic aspirations. But he reveals her to have been an exceptionally lively, intelligent, and dynamic person who had many devoted friends. She was, he argues, a brave lesbian of her times and a person of integrity who remained kind and loyal to most everyone with whom she crossed paths. He suggests that the many denigrating portrayals of her may derive from the deep homophobia of her generation.
She has been accused of fabricating incidents in her memoir and lacing it with half-truths and fantasies. She herself confessed, "I may have made mistakes in some dates or minor incidents but…I feel I have held to the spirit of my statement if not to the letter". Nevertheless, Karen Swenson, a Garbo biographer, and Schanke identified and corrected significant errors in de Acosta's account. While the memoir was initially unsuccessful, it was rediscovered in the late 1960s and widely read in the underground gay community. In spite of its inaccuracies, it is now recognized as an important contribution to gay and lesbian history.
Her poetic work consists mainly of three books published during her life: Moods (prose poems) (1919), Archways of Life (1921), and Streets and Shadows (1922). A comprehensive compilation of these three books appeared, for the first time, in Spanish translation under the title Imposeída (46 poemas) (Las Cruces, NM: Eds. La Mirada, 2016, ISBN 978-0-9911325-4-6), edited by Jesús J. Barquet and Carlota Caulfield. Barquet and Caulfield wrote the introduction to the book ("Mercedes de Acosta en traje de poeta") and, along with Joaquín Badajoz, authored the Spanish translations.
Composer Joseph Hallman memorialized de Acosta in the song cycle, Raving Beauty, for flute, harp, cello, and soprano. The song cycle was based on the correspondence and ephemera held in the de Acosta collection at the Rosenbach Museum. The work deals with her relationships and correspondences with Greta Garbo, Marlene Dietrich, Isadora Duncan, Igor Stravinsky, and others. Commissioned by the Philadelphia International Festival for the Arts, it has been performed many times, including by the Secret Opera.