Stephanie St. Clair was born on December 24, 1897 in Guadeloupe, the French-governed island in the Caribbean. Due to poor record-keeping and, later, urban legends and yellow journalism, there are discrepancies about her origin. Conflicting accounts state her birthplace as Martinique, her birthday was December 25, and birth year was 1887. She was reared by her single mother, Félicienne, who sacrificed much to ensure the upbringing of her daughter. An immediate goal that she had for Stephanie was that her daughter became educated so she worked hard to pay for her schooling.
In 1911, Stephanie St. Clair traveled to the United States, and, according to biographer, Shirley Stewart in The World of Stephanie St. Clair: An Entrepreneur, Race Woman and Outlaw in Early Twentieth Century Harlem, quickly moved on to Canada, where she worked as a domestic servant. Five years later, she returned to America and settled in Harlem, a community in the northeastern section of the borough of Manhattan in New York City. Harlem was quickly becoming settled by African-Americans who had undertaken the mass movement from the South to the North in search of a better quality of life; this movement became known as The Great Migration. Being multilingual in French, Spanish and English strongly aided St. Clair in furthering her educational, personal and professional development.
Approximately ten years later, St. Clair entered the numbers game with a $10,000 investment. By the late 1920s, she, as a policy banker, employed twenty controllers and forty number runners. It has been reported, in sources such as Gangsters of Harlem by Ron Chepesiuk, that St. Clair earned $250,000 annually by that point, thus, making her one of the wealthiest Black women in the United States.