Margaret Olivia Slocum was born September 8, 1828, in Syracuse, New York. Olivia’s father lost his businesses when she was 12 years old and her family life was marked by her father’s financial instability. Her formal education, funded by her uncle, was carried out at the prestigious Troy Female Seminary, alma mater of Elizabeth Cady Stanton, a leader in the 19th century women’s rights movement. Mrs. Sage’s early life intersected with a series of progressive and other movements – Abolitionism, Temperance, Women’s Rights – which, along with the strong influence of the Seminary, played a seminal role in her development.

Mrs. Sage’s biographer, Ruth Crocker, notes, "Feminist historian Anne Firor Scott has argued that Troy Female Seminary … was the center of 'an ever-widening circle' of feminist influence that played a part in the development of an American national culture.” The Seminary was unique in not offering classes dedicated to sewing or housework. Crocker writes, “… the school’s mission was to train girls to earn their own living and thus to ensure their financial independence.” Olivia graduated in 1847, the same year that City College (which did not admit women until 1917) was founded.

Olivia would later work as a teacher and governess, although she was paid poorly and made ill by her heavy teaching load. This lifestyle changed significantly, however, when in 1869, at the age 41, Ms. Margaret Olivia Slocum married Mr. Russell Sage.