William Crowninshield Endicott was born on September 28, 1860 to William Crowninshield and Ellen (Peabody) Endicott, in Salem, Massachusetts. He graduated from Harvard College in 1883. He attended Harvard Law School, and though he did not complete his studies, he passed the Massachusetts bar in 1886. He served as private secretary for his father, then U. S. Secretary of War, before opening a law practice in Salem. Endicott married Marie Louise Thoron in 1889. After another stint in Washington, DC as private secretary for Attorney General Richard Olney, Endicott moved into working for estates and trusts, including his family estate. He became a trustee and later treasurer of the Groton School, was a member of the Essex Institute in 1894, and in 1910 was one of the incorporators and later president of the Society for the Preservation of New England Antiquities. In 1905, he became a trustee, and later an officer and vice-president, of the Peabody Museum in Salem. He was also a founding trustee, vice-president, and president of the Isabella Steward Gardner Museum. And he was also president of the Massachusetts Historical Society from 1926 until his death on November 28, 1936.

Source:

William Crowninshield Endicott Papers, MH 92. Courtesy of Phillips Library, Peabody Essex Museum, Rowley, MA. https://pem.as.atlas-sys.com/repositories/2/resources/650 Accessed September 14, 2023.