Day was born in Brooklyn, although she spent much of her childhood in San Francisco and Chicago; she returned to New York after dropping out of the University of Illinois Urbana-Champaign. There she became very active in socialist causes, especially as a journalist for socialist papers; during this period she had a small handful of affairs and an abortion, but she slowly became more interested in Catholic life, in part because many of the working class with whom she interacted were themselves Catholic. When she became pregnant again, she asked a nun what she could do to have the child baptized; the nun had her memorize the Baltimore Catechism. When her relationship with her partner ended, Day joined the Church herself, and began to write for Commonweal and America.
In 1932 her life changed when she met a French immigrant named Peter Maurin, who showed her how Catholic theology linked up with work for the poor and working class. Together they started the newspaper The Catholic Worker, which became the heart of what has become known as the Catholic Worker Movement. Day died in 1980.
From an editorial in The Catholic Worker, November 1936:
As I waited for the traffic light to change on my way to the Seamen's Defense Committee headquarters, I was idly saying my rosary, which was handy in my pocket. The recitation was more or less automatic, when suddenly like a bright light, like a joyful thought, the words Our Father pierced my heart. To all those who were about me, to all the passerby, to the longshoremen idling about the corner, black and white, to the striking seamen I was going to see, I was akin, for we were all children of a common Father, all creatures of One Creator, and Catholic or Protestant, Jew or Christian, Communist or non-Communist, were bound together by this tie. We can not escape the recognition of the fact that we are all brothers. Whether or not a man believes in Jesus Christ, His Incarnation, His Life here with us, His crucifixion and resurrection; whether or not a man believes in God, the fact remains that we are all children of one Father.
Meditation of this fact makes hatred and strife between brothers the more to be opposed. The work we must do is strive for peace and concordance rather than hatred and strife.
Speaking for myself, I like Dorothy Day very much, and consider this all cheerful news.