Alexander Millar was born on October 24, 1849, in Turriff, Scotland, to Alexander and Jane Millar. He grew up and attended school in Turriff, and he worked as a drapery salesman in Turriff and Glasgow. He immigrated to America around 1872 and settled in Boston, Massachusetts. Soon afterward, he began working as a stenographer with the Union Pacific Railroad.
He married Jane Wilson on May 5, 1875, and they had at least five children: Ethel, born around 1880; William, born around 1882; Bessie, born around 1885; Harold, born around 1887; and Jeanie, born around 1890. In 1887, he became secretary of the Union Pacific Railroad. According to an early biographer, he was an “outspoken advocate of Prohibition…and of woman suffrage.” The family lived in Boston until around 1898, when they moved to Plainfield, New Jersey. He retired from work in the summer of 1917 and purchased a fruit farm in Orange County, New York. He died in Plainfield on March 31, 1918, “after a long illness produced by chronic rheumatism.”