Beaux was born in Philadelphia to Cecilia Leavitt and Jean-Adolphe Beaux. After her mother's death and her father’s return to France, the young Beaux was raised by relatives who encouraged her early artistic activity. By age eighteen, Beaux found success producing commercial lithographs and painting on china while continuing her studies at Philadelphia’s Van der Wielen School of Art and Pennsylvania Academy of the Fine Arts. Beaux traveled to Paris to study at Académie Colarossi, and Académie Julian, including a stint with William-Adolphe Bougereau, a leading painter in the French academic tradition. As Beaux adapted to an Impressionist approach, her work and style invited comparisons to her European and American counterparts including John Singer Sargent, William Merritt Chase, and Mary Cassatt.
After returning to Philadelphia, Beaux was elected an associate member of the National Academy of Design in 1894. One year later, she became the first full-time female instructor at the Pennsylvania Academy of Fine Arts. These appointments, followed by important commissions, enhanced her growing reputation. In 1900 she was awarded the Gold Medal at the Exposition Universelle, Paris. Eight years later, she received an honorary doctorate from the University of Pennsylvania. In 1912, the Corcoran Gallery in Washington, D.C. held a solo exhibition of her work. In 1933, Eleanor Roosevelt presented Beaux with the Chi Omega fraternity's gold medal, for “the American woman who had made the greatest contribution to the culture of the world.”
Important portraits by Beaux include First Lady Edith Roosevelt with her daughter Ethel; George Clemenceau, Prime Minister of France during World War I; and Cardinal Desire-Joseph Mercier, a staunch resister to the German occupation of World War I. For Johns Hopkins she painted Mary Adelaide Nutting and William Henry Howell. Bradley Stevens’ copy of her full-length rendition of John Shaw Billings hangs in the hospital’s Billings Administration Building; the original painting is located at the National Library of Medicine.