Ruth Putnam was one of 11 children of George P. Putnam, founder of the publishing house G.P. Putnam's Sons, and his wife Victorine Haven Putnam. She was born in Yonkers, New York, and grew up in New York City. She earned a degree in literature from Cornell University in 1878 and later was named to its Board of Trustees. She became an historian and wrote biographies of major historical figures such as William the Conqueror, Charles the Bold, Duke of Burgundy, and William the Silent, Prince of Orange. In 1925, she published the collected letters and biography of her older sister Mary Putnam Jacobi, a pioneering woman physician.