William Miller began practicing law in Iowa in 1853. He served as a judge of the Eighth District of Iowa from 1858 to 1862, and a judge of the Circuit Court from 1868 to 1870. During the Civil War, he was a colonel in the Union Army. In 1870 he was appointed to the Iowa Supreme Court, becoming its Chief Justice in 1874. He joined the law faculty at Iowa in 1871, serving as a professor of constitutional and criminal law. Justice Miller was well-known for compiling and editing the Codes of Iowa. He died in 1896.