Florence Ellinwood Allen was born on March 23, 1884 in Salt Lake City. Her mother, Corinne Tuckerman, was a member of the first class admitted to Smith College. Her father, Clarence Emir Allen, was a professor of Latin and Greek at Western Reserve University and placed a strong emphasis on education. Florence took an interest in books from a young age, and her father once said, "If Florence were a boy, I'd make a lawyer out of her." A gifted pianist, Allen moved to Berlin after high school to study music and work as a music critic. She returned to the United States and attended the University of Chicago. In 1913, she received an L.L.B. from New York University Law School.

Allen started her own legal practice in Cleveland, Ohio and was active in the women's suffrage movement. She was the attorney for the Cleveland Woman Suffrage Party and became the first woman to argue before a supreme court, winning a municipal suffrage case in Ohio. She was also active in the Peace Movement in the 1920s. In 1920, the first year women were constitutionally guaranteed the right to vote, she was elected as judge of the Court of Common Pleas, becoming the first woman in history to be elected to a judicial office. In 1922, she was elected to the Ohio Supreme Court, making her the first woman to serve as a judge of the highest court of a state. She served as an Ohio Supreme Court Judge for almost twelve years and in 1934, President Roosevelt appointed her to the Court of Appeals for the Sixth Circuit. No woman had previously been appointed to the United States Court of Appeals.

Judge Allen was a popular lecturer and published several books, including Patris, The Treaty as an Instrument of Legislation, and This Constitution of Ours. She was an outspoken opponent of war and wrote extensively on the topic. She was also interested in international law and was a strong advocate for the International Court. She received numerous honors and awards in her lifetime, including honorary degrees from twenty-five colleges and universities, the National Achievement Award in 1938, the Order of the Coif in 1955 by George Washington University, and a citation for advancing the status of women in the legal profession from the National Association of Women Lawyers. In 1959, a portrait of Judge Allen was given to the United States Court of Appeals for the Sixth Circuit in honor of her contribution to the law. Judge Allen died at the age of eighty-two in her home in Cleveland, Ohio on September 12, 1966.