Mary Heaton was born October 11, 1874, in New York City to Ellen Marvin Heaton and Hiram Heaton. She was raised in prosperity in Amherst, Massachusetts, in a 24-room house with half-siblings from her mother's previous marriage. The money in the family came from her mother's side. In 1852, Vorse's mother married Captain Charles Bernard Marvin, a wealthy shipping magnate and liquor merchant, more than 20 years her senior, when she was a young woman of 18. Ellen Marvin was widowed at age 37 with five children. In 1873, she married Mary's father, who, with his family, operated the Stockbridge Inn.
The family traveled widely, spending over a year in Europe, where Mary attended kindergarten in Hanover and the first year of grade school in Dresden, learning the German language in the process. Later, the family had an apartment in Paris, where Mary learned French, followed later by a winter in Austria.
In her 1935 memoir, she dated her interest in the problems of politics and economics to the years of her youth, when her mother read to her aloud from a book by ethnographer George Kennan on the brutal Siberian penal system of Russia. An interest in classic Russian literature followed, complemented by directed reading with her father on topics of American history.
She found her intellect stimulated by life in the college town of Amherst and discussions held in the family home between her father and several prominent friends from academia, including the president of Massachusetts Agricultural College, Henry Hill Goodell, and anthropology professor John Tyler.
She was allowed to leave the formal school system at a young age and subsequently spent several winters in Paris studying art. In 1896, Heaton began to study at the Art Students' League, on West 57th Street in New York City. The League was established 20 years earlier by strong-minded young men in rebellion from the conservative nature of the instruction at the National Academy of Design. By the time that Mary entered, the school was booming, with over 1100 pupils studying in sex-segregated day and evening classes, studying sketch art, sculpture, and painting.
While Mary found participation in the artistic avant-garde exhilarating, she unfortunately was sadly lacking in talent. She wrote in her diary: "When I come into my room and see my work lying around, my sense of my own futility overwhelms me. After so much work, that is all I can do."
She was young, intelligent, and athletic and was deeply influenced by the ideas of feminism that had begun to emerge as the 19th century came to a close. Many upper-class women such as Mary were in the forefront of the movement for women's rights to economic independence, education, voting rights, and birth control.
Her first husband was Albert White "Bert" Vorse, a widely traveled journalist who had worked for a year in a Boston settlement house, run by Edward Everett Hale. They were married on October 26, 1898 after a brief courtship and had two children: a boy, Heaton, born in 1901 and a girl, Mary, born in 1907.
The couple began to take an increased interest in social problems of the day, spurred by the muckraking reformist politics of the day and a personal friendship with radical journalist Lincoln Steffens. The Vorses would frequently go sailing with Steffens and his wife on the Vorses' boat, where they would be regaled with Steffens's "epic stories" of "gigantic lootings and skulduggeries."
Bert was soon assigned to Paris as the correspondent of the Philadelphia Ledger. It was in France that Mary, encouraged and instructed by her husband, began to try her own hand at professional writing. She began to create and sell romantic fiction to women's magazines. Her stories often featured the motif of a rugged and energetic heroine who managed to win the affection of a coveted male over a more constrained and conventionally feminine rival.
In 1904, the Vorses moved to Venice, where Mary was first introduced into the world of the working class and their labor struggles.
Bert died on June 14, 1910, of a cerebral hemorrhage.
In 1912, she married the journalist Joe O'Brien, a socialist from Virginia whom she met at the 1912 Lawrence Textile Strike. The couple had one child, a boy born in 1914. Joe O'Brien died in 1915.
Vorse was active in the fight against militarism and American entry into World War I and was a founding member of the Woman's Peace Party in January 1915. She was chosen as the delegate of the New York Woman Suffrage Party to an International Women's Peace Congress held in The Hague at the end of April 1915, traveling aboard the MS Noordam through mine-strewn waters to attend.
She wrote for the New York Post, New York World, McCall's, Harper's Weekly, Atlantic Monthly, The Masses, New Masses, New Republic, and McClure's Magazine as well as various news services.
She participated in and reported on the Lawrence Textile Strike, the steel strike of 1919, the textile workers strike of 1934, and coal strikes in Harlan County, Kentucky.
From 1919 to 1923, Vorse was in a relationship with the radical political cartoonist and Communist Party functionary Robert Minor.
Four years before her death in 1966, the 88-year-old Vorse entered the silver jubilee banquet of the United Auto Workers, accompanied by union leader Walter Reuther. There, she received the first UAW Social Justice Award, with former First Lady Eleanor Roosevelt and novelist Upton Sinclair looking on to share her honor. Vorse was feted for her work as one of the most important labor journalists of the 1920s and 1930s.
Vorse died of a heart attack on June 14, 1966, at her home in Provincetown, Massachusetts, on the extreme tip of Cape Cod, where she was buried. She was 92 years old.
In addition to her memoir written in 1935, Vorse participated in an oral history project at Columbia University in 1957, an interview that was transcribed and microfilmed by the university.
Vorse also wrote several ghost stories, including "The Second Wife" (1912). The stories were later collected in the Ash-Tree Press volume Sinister Romance : Collected ghost stories.
Vorse is sometimes remembered anecdotally as the inspiration for the fictional character "Mary French" in John Dos Passos' trilogy USA.