Mary Arthur was born in New York on July 5, 1841. Mary was the sister of future President Chester A. Arthur, nearly twelve years her senior, and the youngest child of William and Malvina Arthur. As a young woman, she married John E. McElroy, with whom she had four children; the family settled in Albany, New York.

Mary Arthur McElroy’s brother, Chester A. Arthur, was a widower when he assumed the presidency in 1881; his wife, Ellen “Nell” Lewis Herndon Arthur, had passed away from pneumonia in 1880. Mrs. McElroy agreed to act as White House hostess during the busy winter social season, returning to Albany in the spring to be with her husband and children. While in Washington, D.C., Mrs. McElroy performed the duties of first lady, hosting well-attended receptions, balls, and dinners while living at the Executive Mansion. Newspapers called her “a general favorite” at the White House.

Mrs. McElroy served as part-time White House hostess until the end of her brother’s administration in 1885. When Chester A. Arthur passed away in 1886, the McElroys became the legal guardians of his daughter, Nell. In the final years of her life, Mary Arthur McElroy expressed her devotion to civil rights while simultaneously opposing women’s suffrage. She passed away on January 8, 1917.