Marion Vaccaro was the daughter of Clara Atwood Black and Rev. Robert M. W. Black, an Episcopal clergyman. Marion attended the Hewlett School on Long Island, NY, and Rosemary Hall in Greenwich, CT, both well-known boarding schools, and then attended the University of Michigan and Smith College. She worked for Florenz Ziegfield and his wife, actress Billie Burke, as a tutor and companion for their daughter, Patricia. She is also listed as a Production Assistant on at least one Hollywood film, in 1958. In 1939, Marion Black married Regis Vaccaro, an alcoholic whose family founded the Standard Fruit and Steamship Company of New Orleans.

Her mother owned the antebellum Key West home, The Trade Winds, where Tennessee Williams rented the slave quarters. Marion and Tennessee Williams met in 1941, and their close friendship continued until her death in 1970. Marion and Williams traveled together extensively during the 1950s and 1960s -- Williams chronicled their travels as the characters Cora and Billy in what he described as his "favorite play", "Two on a Party" (1952). Williams' friendship with Marion led to her being immortalized in some of his other works, as well: he used her maiden name for Flora Goforth's secretary, Blackie, in "The Milk Train Doesn't Stop Here Anymore"; in the play "27 Wagons Full of Cotton", Williams named the superintendent of the Syndicate Plantation Silva Vaccaro; in his work, "Baby Doll", there was a character, Vaccaro; he used the name Regis Vaccaro for the liquor store owner in his play "Thank You, Kind Spirit". Williams dedicated his play "Orpheus Descending" to Marion. Marion is also the subject of a number of papers and essays regarding her friendship with Williams, including “Tennessee and the Banana Queen: The Correspondence of Tennessee Williams and Marion Black Vaccaro” by Philip C Kolin. Correspondence between Marion and Williams are contained in the The Historic New Orleans Collection. Also, poetry and a couple of letters written by Marion Black are part of the Tennessee Williams Papers Collections at Columbia University.