Grace Delafield Day Spier was born in Brooklyn, New York, in 1899, the fourth child of John and Grace Day. In 1904, the family moved to California. Shortly thereafter, they moved to Chicago where they remained until 1916 when the family returned to New York City. All of these moves were occasioned by John Day's career as a sports writer whose speciality was horseracing.
Upon the family's return to New York, Della, the name by which Spier was known throughout her life, took a secretarial course at Eastman's Business College in Poughkeepsie, New York. After graduation, she worked as a secretary for Nevin Sayre, the secretary and later director of the Fellowship for Reconciliation, a Quaker organization. Eventually, she worked with Margaret Sanger, the early-twentieth-century pioneer of birth control, and became an apostle spreading the gospel of birth control. Her sister, Dorothy Day, an American journalist and reformer, co-founded and edited the Catholic Worker. Birth control was a point of contention between Della and her sister Dorothy, a Roman Catholic crusader; despite their differences, the sisters shared a special closeness that remained constant until Della's death.
In 1923, Della went to live with her sister Dorothy in Chicago. That autumn they moved to New Orleans, and, by 1925, they were living in New York. It was through Dorothy that Della entered the political and literary circles of Greenwich Village, where she met Katherine Anne Porter sometime after 1925. Dorothy Day and Porter lived near one another in New York City and had many mutual friends. At this time, Porter was more sympathetic to Communism than Roman Catholicism, although she had been baptized in that faith in 1910. Consequently, her sympathies were more in tune with those of Della than those of Dorothy, a recent and rather devout convert to Catholicism. Della and Porter became fast friends. In August 1927, they were among those who demonstrated in Boston prior to the executions of the two anarchists Nicolo Sacco and Bartolemeo Vanzetti.
In 1928, Porter was living in New York at 561 Hudson Street, in a boarding house which was sometimes referred to as the Caligari House or Casa Calagari, across the street from the Day sisters. In the spring of that same year, Della married Franklin Spier (1896-1973), a Jewish advertising agent and later promotion consultant to book publishers. In 1929, he founded Franklin Spier, Inc., an advertising agency for the publishing trade. In March of that year, Porter joined a group of four expatriate New Yorkers vacationing in Bermuda, two of whom were Della and Franklin Spier. Their vacation was fraught with bad weather and Della's illnesss with her first pregnancy.
Upon their return from Bermuda, the Spiers settled in New York on 17th Street, later moving uptown to 91st and 93rd Streets. From 1935 until 1950, they lived in the Bronx and thereafter in various Westchester County suburbs of New York. They had three children, John Simon, born in 1929; David Houston, born in 1931; and Susanna Day, born in 1935. The demands of her family occupied Della after 1929; however, she never lost her verve for social activism. As late as the early 1950s, she demonstrated with Dorothy against nuclear air raid drills in New York City.
Grace Delafield Day Spier died in April 1980 in Victoria, British Columbia, where she had moved in 1976 to live with her daughter Susanna.