Born in St. Louis, Missouri, Marian O'Shea Wernicke is the oldest of seven children in an Irish Catholic family. At age sixteen, she entered the convent of the Sisters of the Most Precious Blood, a teaching order of nuns. She earned a BA in English from Fontbonne College in St. Louis and began teaching in middle school. Wernicke then volunteered to serve in Lima, Peru, and spent five months in Cochabamba, Bolivia, studying Spanish. For three years she worked in the  Maryknoll parish Nuestra Senora de Guadalupe in Lima, teaching in both grade school and  high school, holding summer activities for teens in the neighborhood, and visiting the families.

In 1971 after returning to the States, she left the convent, and taught in a bilingual program at Holyoke High School in Massachusetts. She later married Michael Wernicke, an electrical engineer, and the couple spent their first year of marriage in Madrid, Spain, where she taught methods in bilingual education to student teachers from from St. Louis University. Upon returning to the States, Marian and her husband settled in Pensacola, Florida, Michael's hometown, where they raised three children, Kristin, Tim, and John. 

After completing  an MA in English at the University of West Florida, Marian joined the faculty in the English department at Pensacola State College, where she taught literature and creative writing, and for six  years served as head of the English/ Communications Department. Upon her retirement , Marian Wrote multiple drafts of her first novel, Toward That Which Is Beautiful, which was published by She Writes Press in 2020. She also published a memoir about her father, called Tom O'Shea: A Twentieth Century Man. Her second novel, Out of Ireland, will be published in April of 2023, by She Writes Press. This novel, historical fiction, is her attempt to imagine and re-create the life of her Irish great-grandmother and her brother who emigrated to the United States in the 1870s. The novel weaves the story of the Irish struggle for independence into the personal struggle of a young woman for her own autonomy.